Question

Identify the variable(s), set up your equation(s), and solve. Richard has an elder sister who is twice his age and a younger sister who is two years younger than him. If the product of his sisters' ages is 70, how old is Richard?

Answer 1

7 years

Explanation:

Given that:

Let Richard's age = x

Elder sister's age = 2x

Youngwr sister's age = x - 2

Product of sisters ages = 70

2x * (x - 2) = 70

2x² - 4x = 70

2x² - 4x - 70 = 0

x² - 2x - 35 = 0

x² - 7x + 5x - 35 = 0

x(x - 7) +5(x - 7) = 0

(x - 7) or (x + 5) = 0

x = 7 or x = - 5

X can't be negative

Hence, x = 7

Richard is 7 years