Math CentralQuandaries & Queries


Question from Lyn, a student:

I would like to know a formula that I would use on a standard calculator to calculate a 30% profit margin on an item.
If I purchased an item at $7.70 how would I calculate 30% profit for me, not just 30% mark up?

Hi Lyn,

You purchased the item for $\$7.70$ and you want to sell it for $\$x$ so that the profit is $30\%$ of $x.$ Hence your cost is $70\%$ of $x.$ Thus

\[0.7 x = 7.70.\]


\[x = \frac{\$7.70}{0.7} = \$11.00.\]


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