### Home > MC2 > Chapter 9 > Lesson 9.3.1 > Problem 9-75

9-75.

Find the amount of money Sasha gained over the 9 months (the interest).

$1003 − $850 = $153

Use the equation *I* = *Prt*, where *I* is the interest, *P* is the principle (original amount she had), *r* is the rate (percent interest per month), and *t* is the time (number of months that have passed).

153 = (850) *r* (9) Solve for *r*.

2% interest