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Math Help - sum of integers

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    sum of integers

    how do i determine the sum of all integers between 1 and 1000 inclusive which are multiples of 5 or 8 or both?
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    Quote Originally Posted by Rose Wanjohi View Post
    how do i determine the sum of all integers between 1 and 1000 inclusive which are multiples of 5 or 8 or both?
    First count the sum of all integers between 1 and 1000 inclusive which are multiples of 5.Call it a.
    Then count the sum of all integers between 1 and 1000 inclusive which are multiples of 8.Call it b.
    Now a+b will have the sum of all integers between 1 and 1000 inclusive which are multiples of 5 and 8, with repetitions. Numbers that are divisible by both 8 and 5 would have occurred in both a and b. Thus 'a+b' has counted multiples of 40 twice. So you will have to subtract the sum of all integers between 1 and 1000 inclusive which are multiples of 40 from 'a+b'.

    So the process is easy if you can answer the following questions:
    1) How to determine the sum of all integers between 1 and 1000 inclusive which are multiples of 5?
    2) How to determine the sum of all integers between 1 and 1000 inclusive which are multiples of 8?
    3) How to determine the sum of all integers between 1 and 1000 inclusive which are multiples of 40?
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