Interest = (Principal)(Rate)(Time)
This is a simple formula for simple interest! The common core standards puts this skill in 7th grade (7.RP.A.3), but students that have a handle on basic percent and substituting for variables can do this and have FUN! I use it in 8th grade for a great end of year project that the kids love to do, it fills at least three days, and makes a great bulletin board. The lesson can easily be simplified for younger students or beefed up for high schoolers.
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