天山 5-20

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A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average (arithmetic mean) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list? B 1/6 C 1/5

mine c

ans b

请指教

topway7

另..20個的平均數為X

所以n=4X

4x/ (4x+20x) = 1/6