Question

Estimate the amount of the tip by rounding the bill to the nearest ten dollars before calculating.

15% tip on a bill of $551.60
The amount of the tip is approximately $

Answer 1

$82.50

Explanation:

This problem requires you round the given bill value, then compute a fraction of that rounded value.

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Rounding

We want to round the bill value to the nearest $10. The digit to the right of the tens digit is 1, so we simply replace that and all digits to the right with zeros. (Had the ones digit been 5 or more, we would increment the tens digit before zeroing digits to its right.)

$551.60 rounded to nearest $10 is $550.00

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Tip Amount

The amount of the tip is found by multiplying the bill by the tip rate.

$550 × 15% = $550 × 0.15 = $82.50

The amount of the tip is approximately $82.50.

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Additional comment

It is often relatively easy to compute a tenth or half of something in your head. We know that 15% = 10% + (1/2)(10%), and that 10% of $550 is $55.

Half of $55 is $27.50, so the tip amount will be $55.00 +27.50 = 82.50, a calculation you can do mentally.