Noor, twelve years old, is three times as old as her sister. How many old will Noor be when she is twice as old as her sister?
Answer: 16
Explanation
Let's denote Noor's current age as N and her sister's current age as S.
Given:
N = 12 years
N = 3S
12 = 3S
S = 4 years
Let's denote the number of years that will pass before Noor is twice as old as her sister as x.
Noor's age = 12 + x
Sister's age = 4 + x
Given:
12 + x = 2(4 + x)
12 + x = 8 + 2x
12 - 8 = 2x - x
4 = x
Noor's age = 12 + 4 = 16
