Math CentralQuandaries & Queries


Question from taha, a student:

A shopkeeper sold a pen for $13.20 to a make a profit 10 percent. In order to earn a profit of 15 percent, he should have sold it for?


Suppose the shopkeeper's cost for a pen is $C. To calculate the profit at 10% he multiplied $C by 0.10 to find the profit and then added it to $C to arrive at $13.20. So his calculation was

$C + 0.10 × $C = 1.10 × $C = $13.20.

Solve this equation for $C and then recalculate the selling price, this time using 15% rather than 10%.

I hope this helps,

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