Question

The mean age of a group of students is 16. John joins the group and the mean age changes to 18. How old is john ?

Answer 1

John is 20 years old.

Explanation:

Given the second mean is 18, it is equal to the first mean age plus John's unknown age. The sum is also divided by 2 because there are 2 values in the sum (1. John's age and 2. the mean, 16 yrs old).

Set up an equation:
`(x+16)/(2)=18`

multiply both sides by 2:
`x+16=36`

simplify:
`x=20`