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

Mathematics
JAMB 2011

Find the sum of the first 18 terms of the series 3, 6, 9,..., 36.
  • A. 505
  • B. 513
  • C. 433
  • D. 635
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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

There is an explanation video available below.


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Explanation Video

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WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
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WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts