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Find the sum of the first 20 terms of the series 8, 12, 16, .....,...

Mathematics
JAMB 2005

Find the sum of the first 20 terms of the series 8, 12, 16, ....., 96

  • A. 1400
  • B. 1040
  • C. 960
  • D. 920
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Correct Answer: Option D
Explanation

8, 12, 16, .....96
a = 8, d = 4, l = 96, n = 20
\(S_{20} = \frac{n}{2}(2a + (n-1)d\)

\(S_{20} = \frac{20}{2}((2\times 8) + (20-1)\times 4)\)

\(S_{20} = 10(16 + (19\times 4)) = 10 \times 92\)

=920

There is an explanation video available below.


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Explanation Video

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