NCERT Solutions class-11 Maths Exercise 6.1

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Exercise 6.1

1. Solve when:

(i) is a natural number

(ii) is an integer

Ans. Given:

Dividing both sides by 24,

(i) When is a natural number then values of that make statement true are 1, 2, 3, 4. The solution set of inequality is {1, 2, 3, 4}.

(ii) When is an integer then values of that make statement true are The solution set of inequality is


2. Solve when:

(i) is a natural number

(ii) is an integer

Ans. Given:

Dividing both sides by

(i) When is a natural number then values of that make statement true are none.

(ii) When is an integer then values of that make statement true are The solution set of inequality is


3. Solve when

(i) is an integer

(ii) is a real number

Ans. Given:

(i) When is an integer then values of that make statement true are The solution set of inequality is

(ii) When is a real number then solution set of inequality is


4. Solve when:

(i) is an integer

(ii) is a real number

Ans. Given:

(i) When is an integer then values of that make statement true are The solution set of inequality is

(ii) When is a real number then solution set of inequality is


Solve the inequalities in Exercises 5 to 16 for real

5.

Ans. Here

Therefore, the solution set is


6.

Ans. Here

Therefore, the solution set is


7.

Ans. Here

Therefore, the solution set is


8.

Ans. Here

Therefore, the solution set is


9.

Ans. Here

Therefore, the solution set is


10.

Ans. Here

Therefore, the solution set is


11.

Ans. Here

Therefore, the solution set is


12.

Ans. Here

Therefore, the solution set is


13.

Ans. Here

Therefore, the solution set is


14.

Ans. Here

Therefore, the solution set is


15.

Ans. Here

Therefore, the solution set is


16.

Ans. Here

Therefore, the solution set is


Solve the inequalities in Exercises 17 to 20 and show the graph of the solution in each case on number line:

17.

Ans. Here

The solution set is


18.

Ans. Here

The solution set is


19.

Ans. Here

The solution set is


20.

Ans. Here

The solution set is


21. Ravi obtained 70 and 75 marks in first two unit tests. Find the minimum marks he should get in the third test to have an average of at least 60 marks.

Ans. Let the marks obtained by Ravi in third test be

According to question,

Therefore, minimum marks needed to be obtained by Ravi is 35.


22. To receive Grade ‘A’ in a course, one must obtain an average 90 marks or more in five examinations (each of 100 marks). If Sunita’s marks in first four examinations are 87, 92, 94 and 95, find minimum marks that Sunita must obtain in fifth examination to get Grade ‘A’ in the course.

Ans. Let the marks obtained by Sunita in fifth examination be

According to question,

Therefore, minimum marks needed to be obtained by Sunita is 82.


23. Find all pairs of consecutive odd positive integers both of which are smaller than 10 such that their sum is more than 11.

Ans. Let and be two consecutive odd positive integers.

and

and

and

and 7

Therefore, the required pairs of odd positive integers are (5, 7) and (7, 9).


24. Find all pairs of consecutive even positive integers, both of which are larger than 5 such that their sum is less than 23.

Ans. Let and be two consecutive even positive integers.

and

and

and

and 10

Therefore, the required pairs of even positive integers are (6,8), (8 10) and (10, 12).


25. The longest side of a triangle s 3 times the shortest side and the third side is 2 cm shorter than the longest side. If the perimeter of the triangle is at least 61 cm. Find the minimum length of the shortest side.

Ans. Let the length of the shortest side be cm.

Length of longest side = cm and length of third side = cm

Perimeter of triangle = = cm

Now,

Therefore, the minimum length of shortest side is 9 cm.


26. A man wants to cut three lengths from a single piece of board of length 91 cm. The second length is to be 3 cm longer than the shortest and the third length is to be twice as long as the shortest. What are the possible lengths of the shortest board if the third piece is to be at least 5 cm longer than the second?

Ans. Let the length of the shortest side be cm.

Length of the second board = cm and length of third side = cm

Now, and

and

and

and

Therefore, minimum length of shortest board is 8 cm and maximum length is 22 cm.


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