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WAEC 2022 · Paper 2 · Q5

Weight (N) 40–46 47–53 54–60 61–67 68–74 75–81 82–88 89–95
Frequency 5 2 3 8 7 6 8 1

The table shows the distribution of weights (N) of students in a class.

  1. (a)

    Using an assumed mean of 71, calculate, correct to one decimal place, the mean weight of the students.

Worked solution (try it first)
  1. Class marks 43,50,57,64,71,78,85,9243, 50, 57, 64, 71, 78, 85, 92 and d=x−71d = x - 71: −28,−21,−14,−7,0,7,14,21-28, -21, -14, -7, 0, 7, 14, 21.
  2. ∑fd=−140−42−42−56+0+42+112+21\sum fd = -140 - 42 - 42 - 56 + 0 + 42 + 112 + 21
    =−105= -105 and ∑f=40\sum f = 40.
  3. Mean =71+−10540= 71 + \dfrac{-105}{40}
    =71−2.625= 71 - 2.625
    =68.375= 68.375
    ≈68.4\approx 68.4 N.

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