Answer:
$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.