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?

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

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.