Question 57
Out of four numbers the average of the first three is 16 and that of the last three is 15. If the last number is 21 then the first number is:
Solution
let the four numbers be a,b,c,d
given that the average of first 3 numbers is 16
i.e; (a+b+c)/3=16
average of last three numbers is 15
i.e; (b+c+d)/3=16
given that last number is 21
therefore b+c+21=16$$\times\ $$3
b+c=48-21
b+c=24
we know that a+b+c=48
=>24+a=48 (since b+c=24)
therefore a=24
hence answer is option D
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