Question

Teddy has two sisters. One of them is 3 years older than Teddy, the other one is 7 years younger than her only brother. How old was the older sisters when the younger sister was born

Answer 1

Lets let Teddy be x.

Sister 1: x+3

Sister 2: x-7

If we subtract the younger sister (sister 2) from the older sister (sister 1), we get:

x+3 - (x-7) = x+3 - x + 7 = 10

The older sister was 10 years old when the younger sister was born.