SOLUTION: Frank is eight years older than his sister. In three years he will be twice as old as she is. How old are they now?

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Question 1147795: Frank is eight years older than his sister. In three years he will be twice as old as she is. How old are they now?
Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


(1) Algebra....

let x be his sister's age
then x+8 is his age

His sister's age 3 years from now will be x+3; his age 3 years from now will be x+11.

3 years from now, his age will be twice his sister's age:

x%2B11+=+2%28x%2B3%29

Solve using basic algebra (I leave that to you).

(2) Logical reasoning....

Since the difference in their ages is 8 years, Frank will be twice as old when he is 16 and his sister is 8. Since that will be 3 years from now, their current ages are 13 and 5.