Answer:
11
Step-by-step explanation:
First, write an equation to represent the situation.
34 = 2a + 12
This equation works because your combined age is half of 68, so 34. If your age is a, then yours sister's age is a + 12. if you add your age to your sister's, you get 2a + 12.
Now just solve for a.
34 = 2a + 12
First, subtract 12 from both sides.
22 = 2a
Then divide both sides by 2.
11 = a
So you are 11 years old. If you need to check your work, your age (11) plus your sister's age (11 + 12, which is 23) is 34, which is half of your grandfather's age.
