Using mental math, the approximate tip to leave for a bill of $81.79, if you tip 15% would be _____..

To estimate 15% of $81.79, find 10% (about $8.18) and 5% (about $4.09), then add them: $8.18 + $4.09 = $12.27. Rounded to the nearest ten cents, that is about $12.30, the choice that matches.

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