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For the grouped data 0–10: 4, 10–20: 6, 20–30: 10, 30–40: 12, 40–50: 8 (class interval: frequency), find the mean using class marks.

Competition practiceData & Probability
  • A28.5
  • B27.5
  • C29.5
  • D30

Step-by-Step Solution

Class marks are 5, 15, 25, 35, 45. Σfx = 5(4) + 15(6) + 25(10) + 35(12) + 45(8) = 20 + 90 + 250 + 420 + 360 = 1140. Σf = 40, so the mean is 1140 ÷ 40 = 28.5.
Answer: A) 28.5

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