Answer :
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.
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.