What percentage of numbers from 1 to 70 have 1 or 9 in the units digit?

Correct answer: 20

Solution

In every set of 10 consecutive numbers, exactly 2 numbers end in 1 or 9. From 1 to 70 there are 7 such sets, so the count is 14. Therefore, the percentage is \(\frac{14}{70}\times 100 = 20\%\).

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