Taro has a sister named Hanako who is 3 years younger than Taro.
At present, the age of Taro's father is 5 times as the sum of the age of Taro and Hanako.
Seven years later, the age of the father becomes 2 times of the sum of the age of Taro and Hanako.
How old is Taro now?
Answer
5 years old
Solution
When Taro's age is set to be X, Hanako's age is to be X-3 and his father's age is (X + X - 3) ×5 = X × 10 -15.
Seven years later father's age will be x ×10 -15 + 7 = X × 10 - 8, Taro is X + 7, and Hanako is X - 3 + 7 = X +4.
X + 7 + X + 4 = X × 2 + 11
(X × 2 + 11) × 2 = X × 4 + 22
X × 10 - 8 = X × 4 + 22
X × 6 = 30
Thus X = 5.
