Question

Mary is half of her sister's age. The sum of their
ages is 18. How old is her sister?

Answer 1

12 years

Explanation:

12/2 = 6

12 + 6 = 18

Answer 2

Mary's sister is 12 years old.

Explanation:

If Mary is half of her sister's age, her sister is 2 times her age.

Represent M as Mary's age...

M+2m=18

3m=18

3m/3=18/3

m=6

But because Mary is a half of her sister's age...

6*2=12