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Find the sum of the first 18 terms of the series 3, 6, 9,…, 36.

Find the sum of the first 18 terms of the series 3, 6, 9,…, 36.
  • A.
    505
  • B.
    513
  • C.
    433
  • D.
    635
Correct Answer: Option B
Explanation

3, 6, 9,…, 36.
a = 3, d = 3, i = 36, n = 18
Sn = (frac{n}{2}) [2a + (n – 1)d
S18 = (frac{18}{2}) [2 x 3 + (18 – 1)3]
= 9[6 + (17 x 3)]
= 9 [6 + 51] = 9(57)
= 513

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