[問題]OG(11th)PS-Q240

[凱薩琳]

Seed mixture X is 40 percent ryegrass and 60 percent bluegrass by weight; seed mixture Y is 25 percent ryegrass and 75 percent fescue. If a mixture of X and Y contaons 30 percent ryegrass, what percent of the weight of the mixture is X?

(A)10%
(B)33 1/3%
(C)40%
(D)50%
(E)66 2/3%

Ans:B

[scujean]

[解]題目最後要問X/[x+y]----（1） 想辦法找x,y的關係式
題目說x裡有0.4的r和0.6的p,且y裡有0.25的r和0.75的f
所以r在x裡的含量=0.4*x 且r在y裡的含量=0.25*y 今天把x,y混和後題目說有0.3的r→x,y混和裡的r含量=0.3[x+y]
利用x個別的r含量+y個別的r含量=混和後的r含量→0.4x+0.25y=0.3[x+y]
→x=05.y帶入（1）

[凱薩琳]

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