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If the n ^ th term of a sequence is 2 n+5 7 , then what is the sum of its first 140 terms?

Options

  1. A2840
  2. B2780
  3. C2920
  4. D5700

Correct answer

C. 2920

Step-by-step solution

Given, t _ n = 2 n +5 7 Since, t ₁₄₀= 2 140+5 7 = 285 7 t ₁= 2 1+5 7 = 7 7 Now, S ₁₄₀= 140 2 ( t ₁+ t ₁₄₀ )=70 ( 7 7 + 285 7 )=2920

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