More Percent Problems

Mental Short Cuts

Motivation Problem

Mentally Compute the Solution to the Following Problem

A restaurant bill is $48. If a person leaves a 15% tip, how much should the person tip?

Since 15% is 10% plus 5% and 5% is half of 10%, we could first take 10% of $48 and then add half as much. Since 10% is the same as one-tenth, one-tenth of $48 is $4.80. We only needed to move the decimal point one place value position. One-half of $4.80 is $2.40. Since 4.80 + 2.40 = 7.20, the person should leave a tip of about $7.20.

This problem motivates the use of compatible values to more easily compute solutions to percent problems mentally. In this session, we consider shortcuts to computing percent problems some of which lead to mental shortcuts.

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