prep2题数学，找不到解释，求助！！

sswat88

A student worked for 20 days.  For each of the amounts shown in the first row of the table, the second row gives the number of days that the student earned that amount.  What is the median amount of money that the student earned per day for the 20 days?
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(A) $96
(B) $84
(C) $80
(D) $70
(E) $48

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?
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(A) Four
(B) Six
(C) Nine
(D) Ten
(E) Eleven

hikiliu

需要图片吗？

sakyamomo

20天么  20天的中数就是第10天 11天赚的钱的平均数  根据图  第10天 11天都是84块 所以答案选84  你把中数跟平均数的概念好好看看就能搞定这类题了

sakyamomo

第二题也是的 是1。5个标准方差 就是那个deviation  一个deviation是0.3 1.5个就是0.45

是建立在mean上的 mean是8.1  就是大于8.1-0.45        小于8.1+0.45  就11个 好像我记得只有第一个是范围外的 我才做的这2题~