几道数学题请教一下

mchen224

 

Q18:

A certain characteristic in a large population has a distribution that is symmetric about the mean m.  If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m +
                d ?

A.      16%

B.      32%

C.      48%

D.     84%

E.      92%

Q24:

The positive numbers w, x, y, and z are such that x is 20 percent greater than y, y is 20 percent greater than z, and w is 20 percent less than x.  What percent greater than z is w ?

 

A.     15.2%

B.     16.0%

C.     20.0%

D.     23.2%

E.      24.8%

24题应该怎么列这个等式关系的呀？ 麻烦了

cathyzq

Q18:

A certain characteristic in a large population has a distribution that is symmetric about the mean m.  If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m +
                d ?

A.      16%

B.      32%

C.      48%

D.     84%

E.      92%

--》你肯定没有看清题目，这道题我在做TT时也做错了，因为我没读懂，其实看透了问题就好了，就是小于M+D的区间，我没办法画分布图，如果可以画的话马上明白，

68%是什么区间是 [m-d,m+d]的区间，所以这以外的分布图就占32%，那么正负两边就是16%

求<m+d，那么就是m的左半边和右半边到m+d的位置，就是50%+34%=84%--》D

后面一题，X=1.2Y;Y=1.2Z,W=0.8X-->要求W和Z的关系，这里有一点要提醒的是问句，THAN后面的那个是BASE就是比较后被除的，我在TT20套里就错了一道关于SENIOR SALES和JUNIOR SALES比较多拜访了多少次除数搞错了，就导致结果错了，而且我觉得ETS也乐得出这种题目迷惑我们。

求出15.2% by W=0.8x=0.8*1.2y=1.2*0.8*1.2z=1.152z

(1.152z-z)/z=15.2%-->A