求解 GWD白皮书（上）第2套 MATH 一题

verygong

GWD白皮书（上）第2套 MATH Q18

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%
  这道题没读懂 麻烦各位大NN 指教下  谢谢！

verygong

还有一题  MATH Q23

Q23:
  The toll for crossing a certain bridge is $0.75 each crossing.Drivers who frequently use the bridge may instead purchase a ticker each month for $13 and then pay only $0.3 each crossing during that month .If a particular driver will cross the bridge twice on each of x days next month and will not cross the bridge on any other day,what is the least value of x for which this driver can save money by using the sticker?
  A 14
  B 15
  C 16
  D 28
  E  29
  这道题我列的方程是这样的  0.75*2-(13+0.3*2)  可算下来不对 麻烦大N 指教

chouliulu

第一个答案是84%吗？第2个是15吧？？

cheryong

第一个是84%，画图，median是在50%的位置，标准公差范围就是M的左边34%+右边34%

verygong

是的 能解释下吗？读不懂题 谢谢哦

nickynicky

第二题的15是怎么出来的阿，谢谢

nickynicky

想明白了，问的是最少使用这个卡多少天，才能省钱，也就是说：

X>=13/(0.75*2-0.3*2)