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Math Help - Arithmetic progression

  1. #1
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    Arithmetic progression

    Given an arithmetic progression -10,-5,0,........State three consecutive terms in this progression whose sum is 90.
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    Quote Originally Posted by mastermin346 View Post
    Given an arithmetic progression -10,-5,0,........State three consecutive terms in this progression whose sum is 90.
    You know that the difference d = 5.

    Your three terms are therefore x, x + 5, x + 10.


    You know they add up to 90.

    So x + x + 5 + x + 10 = 90

    3x + 15 = 90

    3x = 75

    x = 25.


    So your three numbers are 25, 30, 35.
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    Quote Originally Posted by Prove It View Post
    You know that the difference d = 5.

    Your three terms are therefore x, x + 5, x + 10.


    You know they add up to 90.

    So x + x + 5 + x + 10 = 90

    3x + 15 = 90

    3x = 75

    x = 25.


    So your three numbers are 25, 30, 35.
    the three numbers are 25,30,35 or plus 25?=25,50,75?
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  4. #4
    Senior Member nikhil's Avatar
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    aliter

    sum of n terms of A.P is given by
    (n/2)(2A+(n-1)d)
    here n= number of terms
    A= first term
    d= common difference
    in given problem
    n=3,d=5 so putting in equation we get
    (3/2)(2A+10)=90
    2A+10=60
    A=25
    since first term is A=25 other terms will be 30 and 35
    so three terms are 25,30,35
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