The answer is pretty simple, in my opinion. You don't need almost any calculations. 1000 has only 2 distinct factors - 2 and 5. It is obvious that there are 500 odd and even numbers from 1 to 1000. Exclude 1000 (even number) you will have 500 odd numbers and 499 even numbers. And there are 200 multiples of 5 between 1 and 1000 (1000/5). 100 of them are odd numbers (5, 15, 25 etc.) and 100 of them are even numbers (10, 20, 30 etc.). Exclude 1000 - you will have 100 and 99 respectively. (p.s. you
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