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JAMB Mathematics 1995 Question 17

Question 17

Progressions

The 4th term of an A.P is 13 while the 10th term is 31. Find the 21st term.

  1. A.175
  2. B.85
  3. C.64
  4. D.45
Show the answer and explanation

Answer: C (64)

Explanation

a + 3d = 13 and a + 9d = 31, so 6d = 18, d = 3 and a = 4. The 21st term is a + 20d = 4 + 60 = 64.