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Average problem

by MubbashirAbbas » Wed May 23, 2012 10:29 am
In a set of four numbers, the average of the first two numbers is 50, average of last two is 80 and average of middle two is 100. What is the average of the first and last number ??

A) 60 b) 45 c) 30 d)15
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by neelgandham » Wed May 23, 2012 10:42 am
Let a,b,c,d are the numbers in the set(in order). Then according to the question

(a+b)/2 = 50 -(1)
(c+d)/2 = 80 -(2)
(b+c)/2 = 100 -(3)
(a+d)/2 = ?

Equation (1) + (2) - (3)
(a+b)/2 + (c+d)/2 - (b+c)/2 = 50+80-100
(a+d)/2 = 30

IMO C
Anil Gandham
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by MubbashirAbbas » Wed May 23, 2012 10:54 am
Anil,
Could u please mention the logic. You added the first two and subtracted the last. Please explain why ?
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by MubbashirAbbas » Wed May 23, 2012 10:55 am
Anil,
Thanks i got the logic :)
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