Question

9) John and Sarah are each saving money for a car. The total amount of money John will

save is given by the function J = 28 + 4x.
The total amount Sarah will save is given
by the function S = x2 + 2x + 20. After
how many weeks, x, will they have the same amount of money saved? Explain how you arrived at your answer.

Answer 1

To find out how many weeks it will take for John and Sarah to save the same amount of money, we must set their respective functions equal to each other and solve for x.

J = S

28 + 4x = x2 + 2x + 20

x2 + 2x - 4x - 8 = 0

x2 - 2x - 8 = 0

(x - 4)(x + 2) = 0

x = 4 or x = -2

Since x must be a positive value, the answer is that it will take John and Sarah 4 weeks to have the same amount of money saved.