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Ask questions which are clear, concise and easy to understand.

A potato contains 99% of water which weighs 100gm.It is kept in the sun to dry. Now it becomes 98%.Then what is its weight.

Posted by Suryadev Chippada (Feb 22, 2017 9:58 p.m.) (Question ID: 2479)

why is installing a water purifier that only removes odour and dirt is not enough

Posted by Deepak Somasekar (Feb 22, 2017 8:34 p.m.) (Question ID: 2473)

Find the volume of a cuboid if its surface area is 104sqcm and the ratio of length breadth and height is 2:3:4.

Posted by Rathi Kajal (Feb 22, 2017 2:17 p.m.) (Question ID: 2454)

• Surface Area of a cuboid = 104 sqcm (given)

Ratio of L : B : H = 2 : 3 : 4

Let's assume L = 2x, B = 3x & H = 4x

We know, Surface Area of a cuboid  = 2 (lb + bh + lh) = 2 (2x*3x + 3x*4x + 4x*2x) = 2 (6x2 + 12x+ 8x2) = 2 (26x2) = 52x2

52x= 104 => x2 =  2 => x =  √2

Now the volume of Cuboid = lbh = 2x * 3x * 4x = 24x3 = 24 * (√2)3 = 24 * 2 * √2 = 48√2 cubiccm (Answer)

Answered by Manish Gandhi (Feb 22, 2017 2:34 p.m.)
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• Ans. As ratio is given 2:3:4

Total Surface Area of Cuboid = 104 cm2

Let Length of Cuboid = 2x

Breadth of Cuboid = 3x

Height of Cuboid = 4x

We Know

$$TSA = 2 [lh + lb + bh]$$

=> $$104 = 2[2x\times 3x + 2x\times 4x + 3x\times 4x]$$

=> $$52 = [6x^2 + 8x^2 + 12x^2]$$

=> $$52 = 26x^2$$

=> $$x^2 = 2$$

=> $$x = \sqrt 2$$

So Length = $$2\sqrt 2$$

Breadth = $$3\sqrt 2$$

Height = $$4\sqrt 2$$

Volume of cuboid = $$2\sqrt 2 \times 3\sqrt 2 \times 4\sqrt 2 = 48\sqrt 2cm^3$$

Answered by Naveen Sharma (Feb 22, 2017 2:32 p.m.)
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a solid cuboid dimension 30c×25cm×9cm is melted and cast into 2 identical cubes.find the length of the cubes formed.

Posted by Rathi Kajal (Feb 22, 2017 9:41 a.m.) (Question ID: 2430)

• Ans.  Let the length of cubes formed  = a cm

Volume of Cuboid = 2×volume of cube formed

=> 30×25×9 = 2a3

=> a3 = 15×25×9

=> a3 = 3375

=> a = 15

So length of cubes formed = 15cm

Answered by Naveen Sharma (Feb 22, 2017 9:56 a.m.)
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Keeping yourself down to the earth and being courteous is the best way to be humble.  Explain this line in context with the chapter - The Great Stone Face.

Posted by Debjit Mukherjee (Feb 20, 2017 8:15 p.m.) (Question ID: 2368)

Find the volume of a cube with edge 10 cm .express the value in l .

Posted by Varsha Bhati (Feb 18, 2017 9:57 a.m.) (Question ID: 2279)

• Edge of cube = 10 cm

Volume of cube = (Edge)3

= (10)= 1000 cm3

1 l = 1000 cm3

Therefore, Volume of cube = 1 l (litre)

Answered by Shweta Gulati (Feb 18, 2017 10:55 a.m.)
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what is the difference between sound wave and light wave ?

Posted by Krati Chaturvedi (Feb 17, 2017 8:54 p.m.) (Question ID: 2266)

• The difference between Sound waves and Light Waves are: Sound Waves require a medium where Light Waves do not require a medium

<h3>Sound Waves</h3>

1. Require a medium.

2. Travel with a speed of 332 m/s at 0 C.

3. Are longitudinal waves consisting of compressions and rarefactions.

4. Are of different frequencies, giving notes of different pitches.

5. Do not travel far as their energy is dissipated easily.

<h3>Light Waves</h3>

1. Do not require a medium

2. Travel with a speed of 3 *10m/s.

3. Are electromagnetic waves consisting of varying electric and magnetic fields.

4. Are of different frequencies, resulting in different colors.

5. Can travel through a much greater distance.

Answered by imran khan (Feb 17, 2017 9:54 p.m.)
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If (23x-1+10)÷7=6, then x is equal To?

Posted by Pradhyumn Soni (Feb 17, 2017 6:17 p.m.) (Question ID: 2250)

• Ans. $${{{2^{3x-1}} + 10} \over 7} = 6$$

Cross Multiply, We Get

=> $${{{2^{3x-1}} + 10} }= 42$$

=> $$2^{3x-1} = 32$$

=> $$2^{3x-1} = {2^5}$$

on comparing , we get

=> 3x -1 = 5

=> 3x = 6

=> x = 2

Answered by Naveen Sharma (Feb 17, 2017 6:42 p.m.)
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If (23x-1+10)÷7=6, then x is equal to ?

Posted by Pradhyumn Soni (Feb 17, 2017 6:16 p.m.) (Question ID: 2249)

• Ans. $${{2^{3x-1} + 10 } \over 7 } = 6$$

$$cross \space multiply \space we \space get$$

=> $${{2^{3x-1} + 10 }} = 42$$

=> $$2^{3x-1} = 32$$

=> $$2^{3x-1} = {2^5}$$

By Comparing

=> 3x-1 = 5

=> 3x = 6

=>  x = 2

Answered by Naveen Sharma (Feb 17, 2017 6:37 p.m.)
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The average  of four  successive even number is 23. Then which is the greatest  number  out of the four  numbers?

Posted by Archna Ghundiyal (Feb 16, 2017 8:14 a.m.) (Question ID: 2185)

• Ans. Suppose first number = x

Then Second number = x + 2

Third number = x + 4

Fourth number = x + 6

According to quetion,

$${(x + x+2+x+4+x+6)\over 4} = 23$$

=> 4x + 12 = 92

=> 4x = 80

=> x = 20

Largest Number = 20 + 6 = 26

Answered by Naveen Sharma (Feb 16, 2017 8:38 a.m.)
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Can anyone provide me some analytical questions for the chapter Air and Water pollution ?

Posted by Akanksha Arora (Feb 11, 2017 3:19 p.m.) (Question ID: 2014)

• Question 1:

What are the different ways in which water gets contaminated?

Water gets contaminated by the addition of:
(i) Agricultural chemicals: Farmers use excessive amounts of pesticides and fertilizers to increase crop production. These chemicals get carried away to the water bodies due to rains and floods which lead to water pollution.
(ii) Industrial wastes: Industries release harmful chemical wastes into water sources, thereby polluting them.
(iii) Sewage wastes: Waste materials from kitchens, toilets, and laundry sources are also responsible for contaminating water.

<h1> </h1>

Question 2:

At an individual level, how can you help reduce air pollution?

An individual can reduce air pollution by:
(i) Avoiding the use of cars as much as possible and by using public transport whenever possible.
(ii) By not using vehicles for short distances.
(iii) By using clean fuels such as LPG and CNG instead of diesel and petrol.
(iv) Always disposing the garbage properly and not burning it.
(v) Controlling the emissions from vehicles and household chimneys.

Question 3:

Clear, transparent water is always fit for drinking. Comment.

No. Clear and transparent water is not always fit for drinking. Water might appear clean, but it may contain some disease causing micro-organisms and other dissolved impurities. Hence, it is advised to purify water before drinking. Purification can be done by water purifying systems or by boiling the water.

Question 4:

You are a member of the municipal body of your town.
Make a list of measures that would help your town to ensure the supply of clean water to all its residents.

To ensure the supply of clean water to all residents the following steps must be taken:
(i) The main water source must be built in clean surroundings and should be maintained properly.
(ii) Chemical methods such as chlorination must be used for purifying water.
(iii) The area around water pipes must also be clean.

Question 5:

Explain the differences between pure air and polluted air.

Pure air contains around 78% nitrogen, 21% oxygen, and 0.03% carbon dioxide. Other gases such as argon, methane, ozone, and water vapours are also present in small quantities. When this composition of air is altered by the addition of harmful substances or gases such as nitrogen dioxide, sulphur dioxide, carbon monoxide, and particulate matter, then the air is said to be polluted.

Question 6:

Explain circumstances leading to acid rain. How does acid rain affect us?

Burning of fossil fuels such as coal and diesel releases a variety of pollutants such as sulphur dioxide and nitrogen dioxide into the atmosphere. These pollutants react with water vapours present in the atmosphere to form sulphuric acid and nitric acid respectively. These acids come down with the rain, thereby resulting in acid rain.
Effects of acid rain:
(i) Acid rains damage crops.
(ii) Acid rains corrode buildings and structures especially those made of marble such as Taj Mahal.

Question 7:

Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen

(d) Nitrogen

Question 8:

Describe the ‘Greenhouse Effect’ in your own words.

Greenhouse effect may lead to global warming, i.e., an overall increase in the average temperature of the Earth. Greenhouse effect is caused by greenhouse gases. Examples of greenhouse gases include carbon dioxide, methane, and water vapour. When solar radiations reach the Earth, some of these radiations are absorbed by earth and then released back to the atmosphere. Greenhouse gases present in the atmosphere trap these radiations and do not allow heat to leave. This helps in keeping our planet warm and thus, helps in human survival. However, an indiscriminate increase in the amount of greenhouse gases can lead to excessive increase in the Earth’s temperature leading to global warming.

<h1> </h1>

Question 9:

Prepare a brief speech on global warming. You have to deliver the speech in your class.

Global warming is an increase in the average temperature of the Earth’s surface. It occurs as a result of an increased concentration of greenhouse gases in the atmosphere. The greenhouse gases include carbon dioxide, methane, and water vapour. These gases trap solar radiations released back by the Earth. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an increase in the Earth’s temperature leading to global warming.

Question 10:

Describe the threat to the beauty of the Taj Mahal.

Acid rain is a major threat to the beauty of the Taj Mahal. When acid rains fall on the monument (that is completely made of marble), they react with marble to form a powder-like substance that is then washed away by the rain. This phenomenon is known as marble cancer. Also, the soot particles emitted from the Mathura oil refinery located near Agra is leading to the yellowing of the marble.

Question 11:

Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answered by imran khan (Feb 11, 2017 3:28 p.m.)
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AB = 4.5 cm, BC = 5.5 cm, CD = 4 cm, AD = 6 cm, AC = 7 cm

Posted by garvit jain (Feb 10, 2017 2:06 p.m.) (Question ID: 1980)

• Difine ur problem properly

Posted by imran khan (Feb 10, 2017 2:22 p.m.)
• Ans.  Given:  AB = 4.5 cm, BC = 5.5 cm, CD = 4 cm, AD = 6 cm, AC = 7 cm

To construct: A quadrilateral ABCD

Steps of construction: (a) Draw AB = 4.5 cm.

(b) Draw an arc taking radius 5.5 cm from point B.

(c) Taking radius 7 cm, draw an another arc from point A which intersects the first arc at point C.

(d) Join BC and AC.

(e) Draw an arc of radius 6 cm from point A and draw another arc of radius 4 cm from point C which intersects at D.

(f) Join AD and CD.

It is required quadrilateral ABCD

Answered by Naveen Sharma (Feb 10, 2017 2:31 p.m.)
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Mercury has day in one part and night in other part.Give reason?

Posted by Nageswara Rao (Feb 09, 2017 2:39 p.m.) (Question ID: 1949)

• plz answer its my hw.......i am not able to ans..:(

plzzzzzzzzzzzzzzzzz.........

Posted by Nageswara Rao (Feb 09, 2017 2:51 p.m.)
•

On Mercury temperatures can get as hot as 430 degrees Celsius during the day and as cold as -180 degrees Celsius at night.
Mercury is the planet in our solar system that sits closest to the sun. The distance between Mercury and the sun ranges from 46 million kilometers to 69.8 million kilometers. The earth sits at a comfy 150 million kilometers. This is one reason why it gets so hot on Mercury during the day.

The other reason is that Mercury has a very thin and unstable atmosphere. At a size about a third of the earth and with a mass (what we on earth see as ‘weight’) that is 0.05 times as much as the earth, Mercury just doesn’t have the gravity to keep gases trapped around it, creating an atmosphere. Due to the high temperature, solar winds, and the low gravity (about a third of earth’s gravity), gases keep escaping the planet, quite literally just blowing away.
Atmospheres can trap heat, that’s why it can still be nice and warm at night here on earth.
Mercury’s atmosphere is too thin, unstable and close to the sun to make any notable difference in the temperature.

Space is cold. Space is very cold. So cold in fact, that it can almost reach absolute zero, the point where molecules stop moving (and they always move). In space, the coldest temperature you can get is 2.7 Kelvin, about -270 degrees Celsius.
Sunlight reflected from other planets and moons, gases that move through space, the very thin atmosphere and the surface of Mercury itself are the main reasons that temperatures on Mercury don’t get lower than about -180 °C at night

Answered by imran khan (Feb 09, 2017 8:22 p.m.)
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write 100 by using all the ten digits

Posted by tinkle nagori (Feb 08, 2017 10:21 p.m.) (Question ID: 1929)

• Ans. 100 = 1 + 2 + 3 - 4 + 5 + 6 + 78 + 9

100 = 1 + 2 + 34 - 5 + 67 - 8 + 9

100 = 12 + 3 - 4 + 5 + 67 + 8 + 9

Answered by Naveen Sharma (Feb 08, 2017 10:48 p.m.)
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Why water comes only on our earth and not comes on other planets?

Posted by Abhishek Kumar (Feb 08, 2017 9:37 p.m.) (Question ID: 1928)

• The water that makes Earth a majestic blue marble was here from the time of our planet's birth, according to a <a href="http://www.sciencemag.org/content/346/6209/623">new study of ancient meteorites</a>, scientists reported Thursday.

Where do the oceans come from? The study headed by <a href="http://www.whoi.edu/profile.do?id=asarafian">Adam Sarafian</a> of the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts, found that our seas may have arrived much earlier on our planet than previously thought.

The study pushes back the clock on the origin of Earth's water by hundreds of millions of years, to around 4.6 billion years ago, when all the worlds of the inner solar system were still forming.

Scientists had suspected that our planet formed dry, with high-energy impacts creating a molten surface on the infant Earth. Water came much later, went the thinking, thanks to collisions with wet comets and asteroids.

"Some people have argued that any water molecules that were present as the planets were forming would have evaporated or been blown off into space," said study co-author <a href="http://www.whoi.edu/science/GG/people/marschall/">Horst Marschall</a>, a geologist at WHOI.

For that reason, he said, scientists thought that "surface water as it exists on our planet today must have come much, much later—hundreds of millions of years later."

Answered by imran khan (Feb 09, 2017 8:25 p.m.)
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Choose  correct  alternative

6         272       110

156         ?           20

42          342        72

a.206    b.208     c.210       d.212

And explain  how?

Posted by Archna Ghundiyal (Feb 07, 2017 8:55 a.m.) (Question ID: 1880)

• Ans.

Ans. I think this is the right combinations. All odd prime numbers are multiply with prevous number.

 3*2 = 6 17*16 = 272 11*10=110 13*12=156 29*28 = 812 5*4= 20 7*6 = 42 19*18 =342 23*22 = 506

Answered by Naveen Sharma (Feb 07, 2017 12:28 p.m.)
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Choose  correct  alternative

30      24        48

10        ?          12

20        18         30

a.10          b.15      c.12        d.20

And explain  how?

Posted by Archna Ghundiyal (Feb 07, 2017 8:29 a.m.) (Question ID: 1879)

Aditi was standing  on the ground. After  walking  a distance of 10m. to the west, she went 20m, to the South. From there, she walked  6 m to the West  and 8 m to the North. How far is she from her original place?

Posted by Archna Ghundiyal (Feb 06, 2017 8:56 a.m.) (Question ID: 1855)

• Aditi is 16 m away from her original place.

Answered by Akanksha Arora (Feb 11, 2017 3:16 p.m.)
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• 16 m

Answered by shruti dadhwal (Feb 08, 2017 7:07 a.m.)
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• 16m

Answered by Abhinav Rajput (Feb 06, 2017 10:22 p.m.)
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• 16

Answered by akashi kaikyo (Feb 06, 2017 3:31 p.m.)
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13    14      18

2       3         4

173   205     ?

Choose correct alternative

a. 342         b.341       c.340       d.none

And explain how?

Posted by Archna Ghundiyal (Feb 06, 2017 8:49 a.m.) (Question ID: 1854)

• Ans. (c) 340

(13)2 + (2)2 = 173

(14)2 + (3)2 = 205

(18)2 + (4)2 = 340

Answered by Naveen Sharma (Feb 06, 2017 10:36 a.m.)
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A soap cake is 5.5cm*3.5cm*3cm . What will be the volume of a box containing 150 cakes ?

Posted by Khushi Malik (Feb 05, 2017 7:19 p.m.) (Question ID: 1843)

• Ans. Length of Soap = 5.5 cm

Width of Soap = 3.5 cm

Hegith of Soap = 3 cm
As Soap is in shop of Cuboid

Then Volume of one soap cake =

No of Soap cakes = 150

vomule of box =

Answered by Naveen Sharma (Feb 06, 2017 12:16 p.m.)
Thanks (1)
• The soap cake is of cuboidal shape,

Volume of a soap cake = l x b x h

= 5.5x3.5x3 = 57.75 cm3

Volume of box = No. Of cakes x Volume of a soap cake

= 150 x 57.75 =8662.5 cm3

Answered by Shweta Gulati (Feb 05, 2017 7:28 p.m.)
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summary of the lesson darjeeling

Posted by Abirami Lakshmi (Feb 04, 2017 9:14 p.m.) (Question ID: 1810)

one tree equal to 5 pen , 5 pen equal to ?

Posted by kanishka asliya (Feb 04, 2017 6:30 p.m.) (Question ID: 1806)

• 10 trees

Answered by sahiti alekhya (Feb 05, 2017 11:12 a.m.)
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• Ans. one tree

Answered by Naveen Sharma (Feb 04, 2017 6:32 p.m.)
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A godown is in the form of a cuboid of measures 60m x 40m x 30m. How many cuboidal boxes can be stored in it if the volume of the box is 0.8m3

Posted by Aadity Chauhan (Feb 04, 2017 4:09 p.m.) (Question ID: 1803)

• Number of cuboidal boxes can be stored = Volume of godown / Volume of 1 box

= 60 x 40 x 30 / 0.8

= 72000 x 10 / 8

= 90,000

Therefore, 90000 boxes can be stored.

Answered by Rashmi Bajpayee (Feb 05, 2017 11:24 a.m.)
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• Ans.

=>

Answered by Naveen Sharma (Feb 04, 2017 4:26 p.m.)
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Measures of three angles of a triangle are respectively  (5x+10), (3x+15) and (x+20).Depending upon its angles, what type of triangle  is it? Give  explaination.

Posted by Archna Ghundiyal (Feb 04, 2017 8:41 a.m.) (Question ID: 1792)

• By angle sum property of triangle, the sum of all angles is ${180}^{0}$, So

(5x + 10) + (3x + 15) + (x + 20) = ${180}^{0}$

5x + 10 + 3x + 15 + x + 20 = ${180}^{0}$

9x + 45 = ${180}^{0}$

9x = ${180}^{0}$ - ${45}^{0}$

9x = ${135}^{0}$

x =

Therefore, First angle = 5x + 10 =(5 × 15) + 10 = 75 + 10 = ${85}^{0}$

Second angle = 3x + 15 = (3 × 15) + 15 = 45 + 15 = ${60}^{0}$

Third angle = x + 20 = 15 + 20 = ${35}^{0}$

Since, all the angles of the triangle measures less than ${90}^{0}$, So it is an acute-angled triangle.

Answered by Rupender singh (Feb 04, 2017 12:53 p.m.)
Thanks (1)
• Ans.

=>

=>

=>

Answered by Naveen Sharma (Feb 04, 2017 12:49 p.m.)
Thanks (0)
• We will use angle sum property of triangles.  The sum of all the angles of a triangle should be 180 degrees.

(5x+10)+(3x+15)+(x+20) =180

9x+45=180

9x=135

x=15

So, 5x+10 = 75+10 =85 degrees

3x+15=45+15 = 60 degrees

x+20 = 15+20 =35 degrees

Since all the angles of this triangle measure less than 90 degrees,  therefore it is an Acute-angled triangle.

Answered by Shweta Gulati (Feb 04, 2017 9:31 a.m.)
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What is change in 7 and 8 exam in 2017

Posted by pushkar km (Feb 01, 2017 6:57 p.m.) (Question ID: 1741)

why 8 class mathematics videos are not coming sir or mam

Posted by Edula Hussain Reddy (Jan 30, 2017 7:08 p.m.) (Question ID: 1699)

• We will upload the videos soon. If you have questions regarding any of the subjects, you can post. We would be happy to help you.

Answered by Shweta Gulati (Feb 04, 2017 9:37 a.m.)
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What happens when reflection by a plane, polished surface is

Posted by Praveen Chetalla (Jan 28, 2017 7:03 p.m.) (Question ID: 1654)

• When a rays of light reflected by a plane mirror image formation takes place.

Answered by RAJENDRA SINGH (Jan 28, 2017 7:40 p.m.)
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Following are the car parking charges near a railway station upto

4 hours Rs 60

8 hours Rs 100

12 hours Rs 140

24 hours Rs180

Check if the parking charges are in direct proportion to the parking time

Posted by Shubetsha Shanmugam (Jan 28, 2017 10:22 a.m.) (Question ID: 1644)

• Charges for first 4 hours is Rs. 60.

Charges for next 4 hours (8 hours) is Rs. (60 + 40) = Rs. 100

Charges for next 4 hours (12 hours) is Rs. (100 + 40) = Rs. 140

Charges for next 12 hours (24 hours) is Rs. (140 + 40) = Rs. 180

Since the parking charges are not increasing in direct proportion to the parking time.

So, parking charges are not in direct proportion to the parking time.

Answered by Rupender singh (Feb 04, 2017 1:49 p.m.)
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• Ans . The charges are not increasing in direct proportion to the parking time because

=> $\frac{4}{60}\ne \frac{8}{100}$

So Parking chages are not in Direct Proportion to the parking time.

Answered by Naveen Sharma (Jan 28, 2017 2:46 p.m.)
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What is bitumen?

Posted by Irfan Alam (Jan 27, 2017 5:08 p.m.) (Question ID: 1633)

• Ans. Bitumen is a mixture of Organic Liquids that are highly Viscous, Black, Sticky, Entirely Soluble in Carbon Disulfide, and composed primarily of highly condensed Polycyclic Aromatic Hydrocarbons.

Naturally occurring or crude bitumen is a sticky, tar-like form of petroleum which is so thick and heavy that it must be heated or diluted before it will flow. At room temperature, it is much like cold molasses.

Answered by Naveen Sharma (Jan 27, 2017 5:23 p.m.)
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what is the difference between new delhi and shahjahanabad??

Posted by sn na (Jan 24, 2017 11:03 p.m.) (Question ID: 1596)

•  New Delhi Shahjahanabad Unwalled city, constructed on Raisina Hill, south of Shahjahanabad or Old Delhi Constructed as a walled city with 14 gates, adjoining a fort-palace complex, with the river Jamuna flowing near it Broad, straight streets Mazes of narrow and winding lanes and bylanes and quiet cul-de-sacs Sprawling mansions set in the middle of large compounds Crowded and congested mohallas
Answered by Vikrant Singh (Jan 26, 2017 1:57 p.m.)
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