Question

the average of 8 girls is 15 and the average of 6 girls is 13 find the average of the other two girls with equal age​

Answer 1

21

Explanation:

Since the girls have the same age, let their age be x.
Then, their average is

`(x+x)/(2) = (2x)/(2) = x`

Let
`S_(i)` denote the age of 'i' girls.
Then,
`S_(8) = S_(6) + x + x - eq(1)`

Also, we have,

`(S_(8))/(8) =15 - eq(2)`

`(S_(6))/(6) =13 - eq(3)`

Then eq(2):

(from eq(1) and eq(3))

`(S_(6) + 2x)/(8) =15\\\\(13*6 + 2x)/(8) = 15\\\\78+2x = 120\\\\2x = 120-78\\\\x = 21`

The average of the other two girls with equal age​ is 21