Exercises: Use Units as a Way to Understand Problems and to Guide the Solution of Multi-Step Problems

The simple interest formula is $I = P \times r \times t$, where $P$ is in dollars, $r$ is in 1/year, and $t$ must be in years. If $P = 500$ dollars, $r = 0.06$/year, and $t = 18$ months, first convert $t$ to years: $t =$   ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲   years. Then the interest $I =$   ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲ ̲   dollars.