if 5,a2,a3,-…,a20,145 is an a.p.,Then a2+a20

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if 5,a2,a3,…….,a20,145 is an a.p.,Then a2+a20

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Hailey 2 months 2021-10-05T03:44:48+00:00 1 Answer 0 views 0

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    2021-10-05T03:46:47+00:00

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    Brainly.in

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    nareshbyagari4989

    20.07.2018

    Math

    Secondary School

    +13 pts

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    If a1,a2,a3,……….are in ap such that a1+a5+a10+a15+a20+a24=225, then a1+a2+a3+……….a23+a24 is

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    AJAYMAHICH

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    a1 + a5 + a10 +a15 + a20 + a24 = 225 (given)

    (a1+a24) + (a5+a20) + (a10+a15) = 225 ……………..1

    let first term is a & common difference is d then

    a1 = a , a24 = a+23d , a1+a24 = 2a+23d ……….2

    a5 = a+4d , a20 = a+19d , a5+a20 = 2a+23d …………..3

    a10 = a+9d , a15 = a+14d , a10+a15 = 2a+23d …………..4

    putting 2 , 3 , 4 in eq 1 we get

    3(2a+23d) = 225

    2a+23d = 75 ………..5

    now , a1 + a2 + a3 …………a24 = S24

    S24 = 24/2[2a+(24-10d)]

    =12(2a+23d) ……………6

    from 5 & 6

    S24 = 12*75 = 900

    please mark my answer as brain list

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