rework If P dollars are invested at a simple interest rate r (in decimals), the amount A that will be available after t years is \( \mathrm{A}=\mathrm{P}+\mathrm{Prt} \). if \( \$ 400 \) is invested at a rate of \( 6 \% \), how long will it be before the amount of money available is \( \$ 736 \) ?
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Let's begin by rearranging the formula for simple interest to find \( t \). You know the total amount \( A \), the principal \( P \), and the interest rate \( r \). The formula can be rewritten as: \[ A = P + Prt \] We can express it as: \[ A - P = Prt \] From this, we can isolate \( t \): \[ t = \frac{A - P}{Pr} \] Now plug in the values: - \( A = 736 \) - \( P = 400 \) - \( r = 0.06 \) (as \( 6\% \) in decimal form) So, we have: \[ t = \frac{736 - 400}{400 \times 0.06} \] \[ t = \frac{336}{24} \] \[ t = 14 \] The time it will take for the investment to grow from \( \$400 \) to \( \$736 \) at a \( 6\% \) simple interest rate is \( \boxed{14} \) years.