Dilly is 7 years younger than Dally. In 4 years time she will be half Dally's age. What is the sum of their ages now?

The sum of their ages now is 13

Step-by-step explanation:

Dally's age = x

Dilly's age = x - 7

In 4 years time Dilly will be half Dally's age, therefore:

Dilly's age plus four equals to half of Dally's age plus four,

replacing with the values and variables we know:

x - 7 + 4 = (x + 4) / 2

x - 3 = (x + 4) / 2

2x - 6 = x + 4 (Multiplying by 2 at both sides)

2x - x = 4 + 6 (Like terms)

x = 10 ⇒ x - 7 = 3

The sum of their ages now is 13 (10 + 3)