Math CentralQuandaries & Queries


Question from Tash, a student:

The amount of money in a single year of an investment after P dollars were initially invested is
A = P + Prt, where r is the rate of simple interest. What expression describes P? How much money was initially invested if the account has $\$1000$ one year after the initial investment and the interest rate was 5%?

Hi Tash,

Notice that on the right side of $A = P + Prt$ there is a common factor of $P.$ Pull out this common factor and then solve for $P.$ This will result in an expression for $P.$

For your second question $A = \$1000, t = 1$ (I assume $t$ is in years) and the interest rate $r = 5\% = 0.05.$ Solve for $P.$


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