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How many integers from 100 to 999 contain at least one 2 or at least one 5 as digits?

 Sep 8, 2020
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We use complementary counting: what we don't want. How many options for the first digit? 1,3,4,6,7,8,9=7. Second? 0,1,3,4,6,7,8,9=8. Third? 0,1,3,4,6,7,8,9=8. So 7*8*8=448 in total. There are 900 total 3 digit numbers, so 900-448=452. Ans.

 Sep 9, 2020

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