Why 1 leads far more often than 9: Benford's law of first digits
30seconds
Look only at the first digit of any long list of real-world numbers, such as river areas, populations or the figures in a company's accounts. You'd expect each digit from 1 to 9 to lead about one time in nine. It doesn't.
The digit 1 leads about 30% of the time and the digit 9 only about 5%. This is Benford's law, and it falls out of how things grow by multiplying. Try it on six kinds of numbers, then rescale them to see which ones keep the pattern.
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