The mean age of seven children is 10 years. The ages (in years) of six of the children are 3, 6, 8, 14, 15 and 16. Calculate the age of the seventh child.
Worked solution (try it first)
The total of the seven ages is 7×10=70 years.
The six known ages add up to 3+6+8+14+15+16=62.
So the seventh child is 70−62=8 years old, option C.