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I am currently doing a simple interest assignment using the formula $I=PRT$. I have a question where someone is depositing 12500 dollars into their bank and would like to know how long it will take to reach 15000 dollars with a 4.6% interest rate. I know the interest is 2500 dollars and I need to find the time. The equation I currently have is $T=2500/12500*0.046$

By following PEMDAS, I divide before multiplying. However, the answer I get here (0.0092) doesn't make sense to me because the time unit ($T$) is in years and this appears to be a very short duration. By doing multiplication before division, I get around 4.35 years. This makes more sense but isn't the correct way to do order of operations. Have I missed anything?

Demetrius Hiscox
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  • In these scenarios it helps to be clear with parentheses: you divide both sides of $I = PRT$ by $PR$, so you get $I/(PR) = PRT/(PR) = T$. – Rushy Sep 23 '21 at 20:20

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$$T\neq I\div P\times R.$$

These equations are all equivalent: $$I=PRT$$$$T=I\div P\div R\\T=\frac I{P\times R}\\T=I\div(P\times R).$$ Take your pick.

ryang
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