Question

there are 20 children at a library 6 of the children have an average age of five years the remaining children have an average age of 8 years what is the average age of all the children at the library

Answer 1

20 total

6 have average of 5 years
6 x 5 = 30

20-6 = 14

14 have average of 8 years

14 x 8 = 112

112 + 30 = 142

142 / 20 = 7.1 years

Answer 2

$(6 \times 5) + (14 \times 8) \\ = 142$

$142 \div 20 = 7.1$

Average age of all the children at the library
= 7.1

Hope this helps. - M