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Mean of 15 observation is 42 .in this mean of first 8 observation is 40 and last 8 observation is 44 ,then find the 8th observation?

Posted by Nitin Kumar 7 years, 11 months ago

CBSE > Class 09 > Mathematics

1 answers

Saurav Deka 7 years, 11 months ago

1. Sum of all (15)nos = 15 *42 =630 2. Sum of 1st 8 nos = 40*8 = 320 3 Sum of last 8 nos = 44*8 = 352 Now, (try to understand properly)(think hard) let the 1st no be 'a' 2nd no be 'b' ........and so on. Then, 1st 8 nos will be a,b,c,d,e,f,g and h And Last 8 nos will be h,i,j,k,l,m,n and o *Thus, 8th observation is "h*". So, 15 nos - 1st 8 nos = last 8 nos - (h*) =>(a+b+c+d+e+f+g+h*+i+j+k+l+m+n+o)-(a+b+c+d+e+f+g+h*)=(h*+i+j+k+l+m+n+o)-(h*) => 630-320=352-h* =>630-320-352=-h* =>630-672=-h* =>-42=-h* =>h*= 42 So, 8th observation is 42. If you have any doubt, you can question me. Hope it helps!

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