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

To solve A = P(1 + rt) for r, first isolate (1 +rt) by dividing both sides of this equation by P:

A/P =  1 + rt.

Next, isolate rt by subtracting 1 from both sides:

A/P - 1 = rt

Finally, divide both sides by t:

A/P - 1

= r

    t

This could be written in other formats, such as:

A - P

= r

Pt