Average after dropping a subgroup

EasyStatistics~3m

A book of 5050 positions returns 8%8\% on average this quarter. You cut the 1010 worst positions, which averaged 12%-12\%. What is the average return of the 4040 positions you kept? Give a percent to one decimal.

Show hints (2)+
  1. Work in totals: whole book =50×8=400=50\times8=400; dropped =10×(12)=10\times(-12).
  2. Kept total =400(120)=400-(-120), then divide by the remaining 4040 positions.

Answer

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13 (± 0.001)

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Asked at: IMC, SIG

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