急问一道数学题

Running at their respective constant rates, machine X takes 2 days longer to produce w
widgets than machine Y. At these rates, if the two machines together produce 5/4 w
widgets in 3 days, how many days would it take machine X alone to produce 2w widgets?
A. 4
B. 6
C. 8
D. 10
E. 12
答案是E.

这个题的条件太多,用了好多时间也没有理清思路.

Q30:
Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she
buy?
(1) She bought $4.40 worth of stamps.
(2) She bought an equal number of $0.15 stamps and $0.29 stamps.
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is
sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.
AnswerD

But I choose A . 10*0.29+0.15*10    if choose D, (2) only we can come to know that the equal number in between but not how many ?

设两台机器的rate分别为x y

这样 w/x=w/y+2，又（x+y）×3=5w/4

可以求得x，y用w的表达形式

最后问的是2w/x=？

直接带入就OK了

谢谢楼上的兄弟，双手合十．我的数学有时真是钻牛角尖．我竞然用：Ｗ／Ｘ－Ｗ／Ｘ＋２＝２

想多了．为了迎接月底的考试，我要用一周时间专攻数学，真的不知怎么感谢网上及时帮忙的朋友们对我数学的帮助，我的邮箱是sunny777ca[在] yahoo.com.cn
    

My applications is under way. I have done some comprehensive about Universities and MBA programs in USA.

如果在申请过程有什么需要咨询的just feel free to contact me. I will be only pleased to be in any help.

Best wishes,

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