Question

Shown below are the steps a student took to solve the simple interest formula A = P (1 + rt) for r.

A = P (1 + rt)
A = P + rt
A - P = rt
r = (A - P)/t

Explain the algebraic error in the students work.
Then state how the equation r = (A - P)/t can be modified to produce the correct result.

Answer 1

A = P (1 + rt)
A = P + rt

Take a closer look at this step

Answer 2

Okay?

Answer 3

Do you see the problem with this step?

Answer 4

Let's try to solve it ourselves and then we can compare to see where they went wrong.

A = P(1 + rt)

We're trying to solve for 'r'

What's the first step we would do?
We would want to distribute the P into the parentheses

Are you aware of the distributive property?
a(b+c)
= ab + ac

You have to multiple the coefficient to every term inside the parentheses.

So what do you get when you distribute the P?

A = P(1+rt)
A = ??