If x,y,and k are positive numbers such that [X/(X+Y)]*10+[Y/(X+Y)_数学解答

If x,y,and k are positive numbers such that [X/(X+Y)]*10+[Y/(X+Y)]*20=k,and if x < y,which of the following could be the value of
A.10
B.12
C.15
D.18
E.30

人气：477 ℃　时间：2020-05-26 12:02:26

解答

式子左边=[10+10y/(x+y)]
因为x(10+5)=15
只有D、E待选
又因为positive number,你把E代回去试一下：2x+y=0,肯定是一正一负
所以选D
自己想的,不知道对不对~~