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JAMB Mathematics 1991 Question 29

Question 29

Progressions

Find the sum of the 20 terms in an arithmetic progression whose first term is 7 and last term is 117

  1. A.2480
  2. B.1240
  3. C.620
  4. D.124
Show the answer and explanation

Answer: B (1240)

Explanation

Sum = n/2 × (first + last) = 20/2 × (7 + 117) = 10 × 124 = 1240.