Prep T1-DS-149

[dianechiu]

149. 14908-!-item-!-187;#058&010196
If m, r, x, and y are positive, is the ratio of m to r equal to the ratio of x to y ?

(1) The ratio of m to y is equal to the ratio of x to r.

(2) The ratio of m + x to r + y is equal to the ratio of x to y.

ans:(B)
要怎麼解??請教大家,謝謝
我只看出來條件二: (m+x)/(r+y)=x/y
只有m.r.x.y均為1時辦得到
m/r=x/y=1
所以條件二可以

[vantreal]

條件二: (m+x)/(r+y)=x/y 交叉相乘
x(r+y)= y(m+x)
xr+xy= ym+xy
since x and y are both positive, xy on both sides can be cancelled.
xr=ym
x/y=m/r ---> sufficient 