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The first and last term of a linear sequence (AP) are 6 and 10 respectively. If the sum ...

The first and last term of a linear sequence (AP) are 6 and 10 respectively. If the sum of the sequence is 40. Find the number of terms
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  • A Nth = 3
  • B Nth = 4
  • C Nth = 5
  • D Nth = 6
Correct Answer: Option C
Explanation:
nth term of a linear sequence (AP) = a+(n − 1)d
first term = 6, last term = 10 sum − 40
i.e. a = 6, l = 10, S = 40
S\(_{n}\)= n/2(2a + (n − 1)d or Sn = ÷2 (a + l)
S\(_{n}\)Â = n/2(a + l)
40 = n/2(6 + 10)
40 = 8n
8n = 40
8n = 40
n = 40/8
= 5
The number of terms = 5

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