三道数学题：

yizi

1。[data sufficiency]

for the students in class A, the range of their heights is r cm and the greatest height is g cm. For class B, the range of their heights is s and h. Is the least height of the students in class A greater than the least height of the students in class B?

1)r<s

2)g>h

2. For every positive even integer n, the function h(n) is defined to be the product of all the even integers from 2 to n, inclusive. if p is the smallest prime factor of h(100)+1,then p is?

a)       between 2 and 10

b)       between 10 and 20

c)       between 20 and 30

d)       between 30 and 40

e)       greater than 40

3. three grades of milk are 1 percent, 2percent, and 3 percent fat by volume. if x gallons of the 1 percent grade, y gallons of the 2 percent grade, and z gallons of the 3percent grafe are mixed to give x+y+z gallons of a 1.5 percent grade, what is x in terms of y and z?

a)       y+3z

b)       (y+z)/4

c)        2y+3z

d)       3y+z

e)       3y+4.5z

答案是c,e,a, 我横竖没想通。。。望高手指点。。。

微笑的迪妮莎

小弟出来乍到，先对第三道做解~

X/（X+Y+Z）+2Y/（X+Y+Z)+3Z/（X+Y+Z）=1.5

整理下就变成： 0.5X-0.5Y-1.5Z=0

                  X=Y+3Z

第一道题目没看懂：“the range of their heights is s and h”

h是什么啊？

yizi

谢谢第三道，

s and h 就像上面的 r and g 是同理

微笑的迪妮莎

第一题：Class A范围：（g-r,g）  range 就是最大值减最小值

        Class B范围：（h-s,h)

        要比较两班最矮的即证 g-r>或<h-s

       1)r<s

       2)g>h 推出-g<-h 再叠加1）

       得：r-g<s-h OK

      少任何一个都不行

tonyakira

第2道肯定是E呀

lastjuly

THX 第三道~

dairywanted

同问第二题。

我系大P

第二题我曾经问过, 是我第一次prep中的问题. 这里share一下经验

h(100)=2*4*6*8*10*....*100=2*(2*2)*(2*3)*(2*4)...*(2*50)=2^50*(1*2*3*4...*50)=2^50*50!

而50!这里已经包含所有50以内的因子, 包括质数, 所以, h(100)+1这个数的最小质因数必定是比50大.

希望大家能够明白. 这题的关键是第二部的转化