数学题不会！求助！！帮我讲解一下！！感谢！！！

houyunzhe1734

有两道题：
1.The residents of Town X participated in a survey to determine the number of hours per week each resident spent watching television.The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hours.The number of hours that Pat, a resident of Town X, watched television last week was between 1 and 2 standard deviations below the mean.Which of the following could be the number of hours that Pat watched television last week?



(A) 30

(B) 20

(C) 18

(D) 12

(E) 6

这道题答案里说：題目的數據: 平均數(mean) :21 hrs標準差(standard deviation) : 6 hrs



由Pat 上星期看電視的時間在1~2個標準差之下可得知(between 1 and 2 standard deviations below themean)，時間範圍應該坐落在9hrs~15hrs之間è答案D 符合算出來的要求
但是我看不懂为什么，这种题型的思路是什么呢？

2.Last year, a certain public transportation system sold an average (arithmetic mean) of 41,000 tickets per day on weekdays (Monday through Friday) and an average of 18,000 tickets per day on Saturday and Sunday.Which of the following is closest to the total number of tickets sold last year?



(A)1 million

(B)1.25 million

(C)10 million

(D)12.5 million

(E)125 million


答案是D：可我算出来的是C，答案里的解题过程是这样的：

平均在週一至週五票的銷售量 41,000張è週一到週五總銷售量41,000*5=820,000---設(A)?

平均在週末票的銷售量18,000張è周末總銷售量 18,000*2=36,000----設(B)




=平均每日的銷售量è=34,427
一年銷售量è34,427*365(天) = 12,565,855 è答案D(12.5 million)

我打问号的地方是咋算的呢？

希望大家帮我解答一下，非常感谢！



Last year, a certain public transportation system sold an average (arithmetic mean) of 41,000 tickets per day on weekdays (Monday through Friday) and an average of 18,000 tickets per day on Saturday and Sunday.Which of the following is closest to the total number of tickets sold last year?



(A)1 million

(B)1.25 million

(C)10 million

(D)12.5 million

(E)125 million


答案是D：可我算出来的是C，答案里的解题过程是这样的：

平均在週一至週五票的銷售量 41,000張è週一到週五總銷售量41,000*5=820,000---設(A)?

平均在週末票的銷售量18,000張è周末總銷售量 18,000*2=36,000----設(B)


=平均每日的銷售量è=34,427
一年銷售量è34,427*365(天) = 12,565,855 è答案D(12.5 million)

我打问号的地方是咋算的呢？

希望大家帮我解答一下，非常感谢！


題目的數據: 平均數(mean) :21 hrs標準差(standard deviation) : 6 hrs



由Pat 上星期看電視的時間在1~2個標準差之下可得知(between 1 and 2 standard deviations below themean)，時間範圍應該坐落在9hrs~15hrs之間è答案D 符合算出來的要求
但是我看不懂为什么，这种题型的思路是什么呢？

2.Last year, a certain public transportation system sold an average (arithmetic mean) of 41,000 tickets per day on weekdays (Monday through Friday) and an average of 18,000 tickets per day on Saturday and Sunday.Which of the following is closest to the total number of tickets sold last year?



(A)1 million

(B)1.25 million

(C)10 million

(D)12.5 million

(E)125 million


答案是D：可我算出来的是C，答案里的解题过程是这样的：

平均在週一至週五票的銷售量 41,000張è週一到週五總銷售量41,000*5=820,000---設(A)?

平均在週末票的銷售量18,000張è周末總銷售量 18,000*2=36,000----設(B)



=平均每日的銷售量è=34,427
一年銷售量è34,427*365(天) = 12,565,855 è答案D(12.5 million)

我打问号的地方是咋算的呢？

希望大家帮我解答一下，非常感谢！



Last year, a certain public transportation system sold an average (arithmetic mean) of 41,000 tickets per day on weekdays (Monday through Friday) and an average of 18,000 tickets per day on Saturday and Sunday.Which of the following is closest to the total number of tickets sold last year?



(A)1 million

(B)1.25 million

(C)10 million

(D)12.5 million

(E)125 million


答案是D：可我算出来的是C，答案里的解题过程是这样的：

平均在週一至週五票的銷售量 41,000張è週一到週五總銷售量41,000*5=820,000---設(A)?

平均在週末票的銷售量18,000張è周末總銷售量 18,000*2=36,000----設(B)


=平均每日的銷售量è=34,427
一年銷售量è34,427*365(天) = 12,565,855 è答案D(12.5 million)

我打问号的地方是咋算的呢？

希望大家帮我解答一下，非常感谢！

Koothrappali

均值是21，标准差是6，低于均值一个标准差就是21-6=15，低于均值两个标准差就是21-2*6=9，所以时间在9~15之间。

houyunzhe1734

灰常感谢~~~
那第一题那个标准差的呢~

jjfish191516

先统一单位~~~~【0.041*5+0.018*2】*52=12.532

houyunzhe1734