Question

The square of Mark's age 3 years ago is 6 times the age he will be in 9 years. What is his age now?

Answer 1

15.

Explanation:

Let his age now be x years. Then:

(x - 3)^2 = 6(x + 9)

x^2 - 6x + 9 = 6x + 54

x^2 - 12x - 45 = 0

(x - 15)(x + 3) = 0

x = 15, -3

We ignore the negative so his age now is 15.

Answer 2

Age= 15

Explanation:

Let a be for age at the moment

(a-3)^2 =6(a+9)

a^2-6a+9=6a+54

a^2-12a-45

(a-15)(a+3)

a=15 or a=-3

Age cannot be negative (-)

Therefore

Age =15