数学几道请求帮忙急急急

guo573874201 · 发表于 2011-9-14 05:13:33

1. If 5x = 2y and xy ≠ 0, then is what percent of y?
A.2%
B.4%
C.10%
D.40%选d 我算的是60呀拿错了那
E.50%

2. If positive integer x is a multiple of 6 and positive integer y is a multiple of 14, is xy a multiple of 105?
(1)x is a multiple of 9.
(2) y is a multiple of 25.答案选B

3. Each of the 30 boxes in a certain shipment with either 10 pounds or 20 pounds, and the average (arithmetic mean) weight of the boxes in the shipment is 18 pounds.If the average weight of the boxes in the shipment is to be reduced to 14 pounds by removing some of the 20-pound boxes, how many 20-pound boxes must be removed?
A.4
B.6
C.10
D.20 答案选d 我做的是6 可是做了好几遍也是6 我哪错了呢
E.24

guo573874201 · 发表于 2011-9-15 04:41:39

没人帮吗自己顶一下

guo573874201 · 发表于 2011-9-16 05:02:08

顶一下吧

guo573874201 · 发表于 2011-9-16 05:02:27

顶一下吧

Dingqy · 发表于 2011-9-16 09:14:29

1.x=2/5y所以是40%

2.xy起码是6*14=3*2*2*7本身或它的倍数,若要成为105=3*5*7的倍数还少一个因数就是5，条件中只要带5就行，明白？
3.设最初的30箱中有X箱10磅的，20磅的就是30-X箱
10X+20（30-X）=18*30总磅数相等
X=6。那么20磅的就有24箱

再设变动后20磅的有Y箱，再列一样意义的式子
10*6+20Y=14（6+Y）注意现在的总箱数有改变哦
Y=4。 20磅的就剩4箱了，搬走了20箱

数学几道请求帮忙急急急

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数学几道 请求帮忙 急急急

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数学几道请求帮忙急急急