[讨论] PP-Math

i92

请教各位牛牛，给我个思路，谢谢

 

1.At least 100 students at a certain high school study Japanese. If 4 percent of the students at the school who study French also study Japanese, do more students at the school study French than Japanese?

(1)  16 students at the school study both French and Japanese.

(2)  10 percent of the students at the school who study Japanese also study French.

answer:B

 

2.In the xy-plane, does the line with equation y = 3x + 2 contain the point (r, s) ?

(1)  (3r + 2 - s)(4r + 9 - s) = 0

(2)  (4r - 6 - s)(3r + 2 - s) = 0

answer:C

3.A vending machine is designed to dispense 8 ounces of coffee into a cup.  After a test that recorded the number of ounces of coffee in each of 1,000 cups dispensed by the vending machine, the 12 listed amounts, in ounces, were selected from the data.  If the 1,000 recorded amounts have a mean of 8.1 ounces and a standard deviation of 0.3 ounce, how many of the 12 listed amounts are within 1.5 standard deviations of the mean?   (A) Four  (B) Six  (C) Nine  (D) Ten (E) Eleven

answer:E

4.The rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A present and inversely proportional to the concentration of chemical B present.  If the concentration of chemical B is increased by 100 percent, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

 

(A) 100% decrease  (B) 50% decrease  (C) 40% decrease  (D) 40% increase  (E) 50% increase

answer

5.If n is a positive integer and n² is devisible by 72 then the largest positive integer that must divide n is=?

answer:12

 

东岸老男人

刚做完几道，先说说做过的：

2、我是简单带入：

(1)  (3r + 2 - s)(4r + 9 - s) = 0

直接计算3r+2=s or 4r+9=s  注意原文由y=3x+2

(2)  (4r - 6 - s)(3r + 2 - s) = 0

也一样：4r-6=s  or 3r+2=s 

因为是or，所以都不唯一确定，但是同时考虑下，就OK。

4，看懂题目，是说和平方成正比，所以反比的增加了100%，就是分母增加了2倍，那么正比的就是分子也要同样增加2倍。所以是开根号：根号2=1.41....  所以最接近的就是0.4

[此贴子已经被作者于2008-2-1 11:41:37编辑过]

i92

谢谢东岸老男人

diane320

有没有大牛解释一下剩下的题嘞...