Question

Canada has a population that is about 1/10 as large as the united states. If canadas population is about 32 million, about how many people live in the united states? Explain the number of zeros in your answer.

Answer 1

Call Canada's population $c$, and call the U.S. population $u$.

We see that $c=\frac{u}{10}$.  Substituting 32 million for c, we see that $32,000,000=\frac{u}{10}$.  Multiplying by ten, we see that $320,000,000=u$.  By using Algebra properly, we have ensured that the number of zeroes in our final answer is correct.