请教几题数学~~~谢谢NN们先~~~~

Rainbeauty · 发表于 2011-4-10 21:15:35

If the drama club and music club are combined, what percent of the combined membership will be male?
(1) Of the 16 members of the drama club, 15 are male.
(2) Of the 20 members of the music club, 10 are male.
这题选E的我觉得答案有问题耶：既然都知道了两个club的人数又知道其中多少male 那肯定能算出来了为什么会选到E？难道我题目不是这么理解的？
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What is the average (arithmetic mean) height of the n people in a certain group?
(1) The average height of the n/3 tallest people n the group is 6 feet 2 1/2inches, and the average height of the rest of the people n the group is f feet 10 inches.
(2) The sum of the heights of the n people is 178 feet 9 inches.
这题答案给的A。不理解啊：f不知道是多少加权平均无法算出一个确定的值。。。
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If x and y are positive integers, is xy a multiple of 8 ?
(1) The greatest common divisor of x and y is 10.
(2) The least common multiple of x and y is 100.
答案选C的 totally do not understand >_<...
I will appreciate~~~

barbiebear · 发表于 2011-4-10 21:39:25

供讨论

1. 不知两个club中多少male是相同的。
类似于，知道两个集合A,B, 求AUB。 AUB= A+B-A交B，不知A交B，无法求AUB

3.1) x=10m, y=10n,
2) x,y最大公倍数100，可100=10mg=10nh
两者单独无法确定xy的数值，太多了
结合，可知x,y必不相等
mg=nh=10,
10只有两对因子组合，10,1； 2,5
因此xy,只有两种取值，10,100 或者20,50， xy关系对称，所以严格的说，可以有四对解，不过求的xy,不用考虑具体解
xy总是等于1000，是8的倍数
C

Rainbeauty · 发表于 2011-4-12 18:48:17

but...still cannot understand the second question...

请教几题数学~谢谢NN们先~~

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