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ratio           

A comparison of two quantities by division

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proportion         

an equation that states that two ratios are equal

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unit rate              

A rate with a denominator of 1.

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commission       

An amount paid to an employee based on a percentage of the employee's sales

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discount              

The amount by which the regular price of an item is reduced

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gratuity           tip

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interest       

the price paid for the use of borrowed money

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mark up              

Gross profit / cost of sales x 100