天山 5-20

assfgrtrtr

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

sammen

楼主大概吧是平均数的4倍看成是其他20数和的4倍了，我刚一看，也上当了，只拐自己粗心。

mikejia

设mean=k

sum of the other 20 numbers is 20K. and n=4K

4k/(20K+4k)= 1/6