[問題]GWD 11-17

[honey801106]

Q17

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?

A. 1/20
B. 1/6
C. 1/5
D. 4/21
E. 5/21

the answer is B.
麻煩高手幫忙解題, 謝謝!

[elmer0901]

依題意來說,
可先設為其他20個的平均數為A
則n=4A
20個平均數為A,故可推出其總和為20A
所以n除21個總和=n/n+20A
=4A/24A
=1/6

[honey801106]

謝謝您 :)