Answer
$P=\dfrac{I}{rt}$
Work Step by Step
Divide $rt$ on both sides of the equation to obtain:
$\require{cancel}
\dfrac{I}{rt} = \dfrac{Prt}{rt}
\\\dfrac{I}{rt} = P
\\P=\dfrac{I}{rt}$
This formula gives the principal amount invested.
I = interest, r = time, and r = interest rate
