GWD11-Q17

[凱薩琳]

A certain list consists of 21 different numbers. If n is in the list and n is 4 times the average 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

Ans:B

[sencerio]

總共有21個數字，不管二十個數是怎樣，
二十個數的平均都為x, 則二十個數總合為20x
第21個數字(也就是n)就為4x

所以……(第21個數):(所有21個數字的總合)=4x : (20x+4x)
=4x : 24x
=1:6
也就是1/6