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Question:

flowerelia
flowerelia
Student
High School - 10th Grade

Calculate the sum 1+4+7+....+31.

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Posted by flowerelia on Saturday May 30, 2009 at 7:34 AM and tagged with math, sum.

Answers:

  1. nick12
    nick12 Student
    High School - 10th Grade

    2n-1

    n=16

    16^2=256

    the answer is 256

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    Posted by nick12 on Saturday May 30, 2009 at 7:42 AM

  2. giorgiana1976
    giorgiana1976 Teacher
    Doctorate

    eNotes Editor

    1+(1+3)+(1+2*3)+....+(1+10*3)

    =(1+1+...+1)+3*(1+2+3+...+10)=

    =11+ (1+10)*30/2=11(1+15)=176

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    Posted by giorgiana1976 on Saturday May 30, 2009 at 9:18 AM


  3. fahad-alfahad

    sum = n/2*(a+L) {n=number of term ,a=first term ,L=last term)

    sum = 10/2 * ( 1 + 31 )

    sum = 5 * 32 = 160

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    Posted by fahad-alfahad on Sunday May 31, 2009 at 11:18 PM

  4. aj11
    aj11 Teacher
    Elementary / Primary

    If you see carefully, you can find that this is the sum of arithmetic sequence by the number of 3

    The sum of arithmetic sequence is  n/2*(a+L) {n=number of term ,a=first term ,L=last term)

    Then.10/2 * ( 1 + 31 )=5 * 32 = 160

     

     

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    Posted by aj11 on Tuesday June 2, 2009 at 6:05 PM