問PP數學兩題

[sugarcane]

1.during a 40-mile trip ,Maria traveled at an average speed of x per hour for the first y miles of the trip ans at the average speed of 1.25miles per hour for the last 40-y miles of the trip.The time Maria took to travel 40 miles was what percent of the time it would be taken her if she had traveled at an averge speed of x miles per hour for the entire trip?
1. x =48
2. y=20
我選了D
結果答案是B

2.The resident of Town x participated in a survey to determine the number of hours per week each resident spent watching TV.Thedistribution of the resylt of the survey had a mean of 21 hours ,standard deviation of 6 hours.The number of hours that Pat,a resident of Town X,watched TV last week was between 1 and 2 standard deviation below the mean ,which of the following could be the number of hours that Pat watched TV last weeK?

a.30
b.20
c.18
d.12
e.6
答案是12

不會算耶
標準差也有點忘了

Q3.Ona tour ,the ratio of the number of women to the number of child was 5:2 ,what's the number of men?
1.the ratio of the number the child to men was 5:11
2.The number of women was less than 30

答案是C耶
我選E??
拜託大家了

[cssteph]

Q3.
由題目可知w:c=5:2
(1)c：m=5:11
所以w:c:m=25:10:22
(2)w<30人
所以(1)+(2)可知w即25人，c10人，m22人

我只會第三題^^"

[maxcos]

2. 平均是21 標準差6
問Pat between 1 and 2 standard deviation below the mean
應該是 21-6*2< Ans<21-6 , 7<Ans<15
所以選12

[wing3315]

1.during a 40-mile trip ,Maria traveled at an average speed of x per hour for the first y miles of the trip ans at the average speed of 1.25miles per hour for the last 40-y miles of the trip.The time Maria took to travel 40 miles was what percent of the time it would be taken her if she had traveled at an averge speed of x miles per hour for the entire trip?
1. x =48
2. y=20
我選了D
結果答案是B

本題問的是： 全程原題所花的時間 / 全程只用x速度所花的時間
1.只給我們x=48 , 沒有距離, 所以求不出時間
2.y=20, 所以可以求出原題時間： (20/x)+(20/1.25)
因此, 答案就等於 (20/x)+16 / (20/x) 即可求出%

[chris8888]

Q1.
一共40 miles, 前y miles 速度x, 後40-y miles 速度 1.25x
(1). (y/x + (40-y)/1.25x) / 40/x ; 可代入x=48 ; 可發現, 分子和分母的y不可簡化約分, 以致於無法求出
(2). (y/x + (40-y)/1.25x) / 40/x ; 可代入y=20, 可約分, 以致於算得出
另外因為沒有平方的情形, 所不會有兩種可能性, 答案就是B