Given a number n, count all multiples of 3 and/or 5 in set {1, 2, 3, ... n} - GeeksQuiz

Given a number n, count all multiples of 3 and/or 5 in set {1, 2, 3, ... n} - GeeksQuiz
Given a number n, count all multiples of 3 and/or 5 in set of numbers from 1 to n.

The value of n/3 gives us number of multiples of 3, the value of n/5 gives us number of multiples of 5. But the important point is there are may be some common multiples which are multiples of both 3 and 5. We can get such multiples by using n/15.

unsigned countOfMultiples(unsigned n)

{

   // Add multiples of 3 and 5.  Since common multples are

   // counted twice in n/3 + n/15, subtract common multiples

   return (n/3 + n/5 - n/15);

}

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