In a class there are $24$ boys whose ages is decreased by $4$ months, when new boy aged $20$ years is replaced by a new boy. Find the age of the new boy.

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Solution

Let age of the new boy was $x$ .
Age decreased $= 4$ months $= \frac{4}{12} = \frac{1}{3}$ years
Now, we have formula for this type of questions,
Number of members in the group $\times$ age decreased $=$ difference in ages of boy in and boy out.
$24 \times (\frac{1}{3}) = 20 - x$
$x = 12$ years
Thought process method:
Total age decreased $= 4 \times 24 = 96$ month $= 8$ years
It means the difference of the ages between boy in and out would be $= 20 - 8$ $= 12$ years.

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In a class there are 24 boys whose ages is decreased by 4 months, when new boy aged 20 years is replaced by a new boy. Find the age of the new boy.

In a class there are $24$ boys whose ages is decreased by $4$ months, when new boy aged $20$ years is replaced by a new boy. Find the age of the new boy.