gs1medium

How many numbers from 0 to 999 are not divisible by either 5 or 7?

  1. A.313
  2. B.341
  3. C.686
  4. D.786
▶ Answer & Explanation

Correct answer: C. 686

To find the count of numbers not divisible by 5 or 7, we first find the total numbers (1000, from 0 to 999). Then we subtract the numbers divisible by 5 and the numbers divisible by 7. Using the principle of inclusion-exclusion, we add back the numbers divisible by both 5 and 7 (i.e., by 35) to avoid double-counting. The count of numbers divisible by 5 is 200 (999/5). The count of numbers divisible by 7 is 142 (999/7). The count of numbers divisible by 35 is 28 (999/35). So, numbers divisible by 5 or 7 = 200 + 142 - 28 = 314. Therefore, numbers not divisible by 5 or 7 = 1000 - 314 = 686.

Source: UPSC gs1 2010

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