• Q. First term is of arithmatic progression sequence is 39 and the difference between consecutive numbers is 13 , Find the sum numbers 17th, 18th, 19th, 20th and 21th terms.
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  • Sum of 17 position is (17/2)[2*39 + (17 - 1)x 13 ]

    = (8.5)[78 + (16)x 13 ]

    = (8.5)[78 + 208 ]

    = (8.5)[286]

    ie. S17 = (2431)

  • Sum of 18 position is (18/2)[2*39 + (18 - 1)x 13 ]

    = (9)[78 + (17)x 13 ]

    = (9)[78 + 221 ]

    = (9)[299]

    ie. S18 = (2691)

  • Sum of 19 position is (19/2)[2*39 + (19 - 1)x 13 ]

    = (9.5)[78 + (18)x 13 ]

    = (9.5)[78 + 234 ]

    = (9.5)[312]

    ie. S19 = (2964)

  • Sum of 20 position is (20/2)[2*39 + (20 - 1)x 13 ]

    = (10)[78 + (19)x 13 ]

    = (10)[78 + 247 ]

    = (10)[325]

    ie. S20 = (3250)

  • Sum of 21 position is (21/2)[2*39 + (21 - 1)x 13 ]

    = (10.5)[78 + (20)x 13 ]

    = (10.5)[78 + 260 ]

    = (10.5)[338]

    ie. S21 = (3549)

  • so the sequance of the sum numbers from position are.
    S17 = 2431
    S18 = 2691
    S19 = 2964
    S20 = 3250
    S21 = 3549

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