Question

The average age of a group of 10 children is 10 years. A child leaves the group and average is increased by 1 year. Find the age of that child.

Answer 1

$\Rightarrow$ The average age of a group of $10$ children is $10years$.

$\therefore$ Sum of the age of $10$ children $=(10\times 10)years=100years$

$\Rightarrow$ The, a child leaves the group and average increased by $1$

$\Rightarrow$ So, there will be $9$ children and their average is $11$

$\therefore$ Sum of age of $9$ children $=(9\times 11)years=99years$

$\Rightarrow$ Required age of child $=(100-99)year=1year$