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Math Help - Sum of integers

  1. #1
    Member Rimas's Avatar
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    Sum of integers

    Find the sum of the first twenty odd positive integers that have a remainder of 1 when divided by 3
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  2. #2
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    well you have...

    1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

    are your first 20 odd positive integers.

    the numbers that will give you a remember of 1 when divided by 3 is

    1 + 7 + 13 + 19 + 25 + 31 + 37 = 133
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  3. #3
    Junior Member Godfather's Avatar
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    Quote Originally Posted by smoothi963 View Post
    well you have...

    1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39

    are your first 20 odd positive integers.

    the numbers that will give you a remember of 1 when divided by 3 is

    1 + 7 + 13 + 19 + 25 + 31 + 37 = 133
    u got the whole idea wrong
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  4. #4
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    Hello, Rimas!

    Find the sum of the first twenty odd positive integers
    that have a remainder of 1 when divided by 3

    The numbers are: .7, 13, 19, 25, . . .

    This is an arithmetic sequence with first term a = 7 and common difference d = 6.

    The sum of an A.S. is: .S
    n .= .n[2a + (n-1)d]

    Therefore: .S
    20 .= .(20)[27 + 196] .= .1280

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