Round numbers worth knowing

In an estimation question you are allowed to assume almost anything, as long as you say it and it is reasonable. But a few numbers come up so often that fumbling them costs you credibility. If you say the US has 100 million people, the interviewer stops trusting the rest of your answer, however good the structure.

This lesson gives you a short table of round figures to learn, then the arithmetic habits that stop you dropping zeros. It supports Step 3 (Assume) and Step 4 (Calculate) of the five-step estimate.