Respuesta :

Awesomenooby

Answer:

Mary's sister is 12 years old.

Step-by-step 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

Answer:

12 years

Step-by-step explanation:

12/2 = 6

12 + 6 = 18