Question

5. In a class, there are 20 boys whose average
age is decreased by 2 months, when one boy
aged 18 years is replaced by a new boy. The age of the new boy is?
a. 14 Yr 8 Mon
c. 16 yr 4 Mon
b. 15 Yr
d. 17 Yr 10​

Answer 1

Answer:

Let age of the new boy was X.

Age decreased = 4 months = 4/12 = 1/3 years

Now, we have formula for this type of questions,

Number of members in the Group * age decreased = difference in ages of boy in and boy out.

24 * (1/3) = 20 -X

X = 12 years.

Thought process method:

Total age decreased = 4 *24 = 96 months = 8 years.

It means the difference of the ages between boy in and out would be = 20 - 8 = 12 years.