How many integers between 100 and 300 are multiples of both 5 and 7, but are not multiples of 10?
Solution
The integers that are multiples of both 5 and 7 are the integers that are multiples of 35. The smallest multiple of 35 greater than 100 is . Starting at 105 and counting by 35s, we obtain 105, 140, 175, 210, 245, 280, 315. The integers in this list that are between 100 and 300 and are not multiples of 10 (that is, whose units digit is not 0) are , of which there are 3.
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