Question

a boy is 17 tears old and his sister is twice as old. when the boy turns 23 yrs old what will be the age of his sister?

Answer 1

b=17
s=2b=17(2)=34
so

34-17=17 therefor
s-17=b

so
s-17=23
add 17 to both sdies
s=40
sister will be 40

Answer 2

So,

We know that the boy is half as old as his sister.

Boy now = 17
Sister now = 34

Boy + 6 = 23

So, we add 6 to the sister's current age.
34 + 6 = 40

The sister will be 40 years old.