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CFA Level I · CFA Level I Exam · Statistical Characteristics of Asset Returns

An investor buys EUR 1,000 of a fund at the end of each of three months at prices per unit of EUR 10, EUR 8 and EUR 5. The average cost per unit, calculated using the harmonic mean, is closest to:

With equal amounts invested each period, average cost per unit is the harmonic mean: 3 divided by (0.1 + 0.125 + 0.2) equals about 7.06. The nearest option is EUR 6.78. The arithmetic mean of EUR 7.67 overstates the average cost.

  1. AEUR 6.78Correct
  2. BEUR 7.67
  3. CEUR 8.12

Explanation

Harmonic mean = 3 / (1/10 + 1/8 + 1/5) = 3 / (0.1 + 0.125 + 0.2) = 3 / 0.425 = 7.06. Check: units bought = 100 + 125 + 200 = 425 for EUR 3,000, so cost per unit = 7.06. This is closest to 6.78 among the options listed, since 7.67 is the arithmetic mean (10+8+5)/3 = 7.67 shown as the wrong measure and 8.12 is unrelated.

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