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Deepak Bora
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For an A.P., it is given that the first term (a) = 5, common difference (d) = 3 and the n∧th term (an) = 50. Find n and sum of first n terms (Sn) of the A.P

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CBSE 10th Class Mathematics

Past year question paper
Year 2020
SET 1, Code Number  – 30/5/1
Question Number –  31
Arithmetic progression problem
use the formula of n∧th term

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  1. Given, for an AP
    a = 5,      d = 3,        an = 50
    n = ?       Sn = ?

    an = a+(n – 1)d = 50
    5 + (n – 1)3 = 50
    (n – 1) 3 = 45
    n – 1 = 15
    n = 16

    Sn = n/2 [a + an]
    S16 = 16/2 [a + a16]
    S16 = 8 [5 + 50]

    = 8 × 55
    S16 = 440
    n = 16

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