# Answer to Question #4641 in Calculus for ong

Question #4641

The average mass of 4 boys is 36.5kg.When one boy left,the average mass of the remaining boys is 36kg.What is the mass of the boy who has left?

Expert's answer

Let m1,m2,m3,m4 be the mass of first, second, third and forth boy respectively. Then,

(m1+m2+m3+m4)/4 = 36.5& (*)

(m1+m2+m3)/3 = 36 (**)

As we know from (**),

m1+m2+m3 = 36*3 = 108. Let's substitute is into (*):

(108+m4)/4 = 36.5

Hence, m4 = 36.5*4 - 108 = 38 kg.

So, the mass of the boy who has left is 38 kg.

(m1+m2+m3+m4)/4 = 36.5& (*)

(m1+m2+m3)/3 = 36 (**)

As we know from (**),

m1+m2+m3 = 36*3 = 108. Let's substitute is into (*):

(108+m4)/4 = 36.5

Hence, m4 = 36.5*4 - 108 = 38 kg.

So, the mass of the boy who has left is 38 kg.

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