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JAMB Mathematics 1999 Question 48

Question 48

Measures of Dispersion

The mean of four numbers is 5 and the mean deviation is 3. Find the fourth number if the mean deviation of the first three numbers is 2.

  1. A.6
  2. B.10
  3. C.11
  4. D.12
Show the answer and explanation

Answer: C (11)

Explanation

The four deviations from 5 add to 4 × 3 = 12 and the first three add to 3 × 2 = 6, so the fourth number is 6 away from 5. So it is 11 (the other possibility, −1, is not an option).