求助PREP一道数学题

musicbbt

61. 5157-!-item-!-187;#058&004472

Of the 60 animals on a certain farm, 2/3
            are either pigs or cows. How many of the animals are cows?

(1) The farm has more than twice as many cows as it has pigs.

(2) The farm has more than 12 pigs.

怎么也绕不明白了，2/3
                are either pigs or cows应该怎么理解？

谢谢！

musicbbt

Resident in Town X hold a survey determine number of hours per week they spent in watching TV. The result of survey had a mean of 21 hours and standard deviation of 6 hours. The number of hour Pat spent in watching TV last week was between 1 and 2 standard deviation below the mean. Which of the following could be the number of hours Pat spent on TV last week?
A. 30     B. 20     C 18        D12          E6

masonyxm

第一题好像做到过，选A（20头cows）。60头牲畜中有3分之2不是pig就是cow。

flytomydream

以下是引用musicbbt在2008-4-6 16:43:00的发言：

61. 5157-!-item-!-187;#058&004472

Of the 60 animals on a certain farm, 2/3
   are either pigs or cows. How many of the animals are cows?

(1) The farm has more than twice as many cows as it has pigs.

(2) The farm has more than 12 pigs.

怎么也绕不明白了，2/3
    are either pigs or cows应该怎么理解？

谢谢！

A

就是说2/3要么是猪要么是牛 不会是其他动物

加上1的条件，可以得出牛有40只

flytomydream

以下是引用musicbbt在2008-4-6 16:47:00的发言：
Resident in Town X hold a survey determine number of hours per week they spent in watching TV. The result of survey had a mean of 21 hours and standard deviation of 6 hours. The number of hour Pat spent in watching TV last week was between 1 and 2 standard deviation below the mean. Which of the following could be the number of hours Pat spent on TV last week?
A. 30     B. 20     C 18        D12          E6

答案是D吗？

我认为就是选在21-6与21-6*2之间的数字啊

musicbbt

动物那道题正确答案是C，我也是选了A,所以我觉得我是没看明白题

后面那道题，谢谢楼上了，你一说我茅塞顿开了，还一直在琢磨着代标准差的公式呢

flytomydream

以下是引用musicbbt在2008-4-6 19:24:00的发言：

动物那道题正确答案是C，我也是选了A,所以我觉得我是没看明白题

后面那道题，谢谢楼上了，你一说我茅塞顿开了，还一直在琢磨着代标准差的公式呢

我发现了 那句话的意思是the total number of cows and pigs is 40, which is 2/3 of 60

所以要1和2加在一起才能得出cow的数量

就是C。。。

xlyun

以下是引用flytomydream在2008-4-6 17:53:00的发言：

答案是D吗？

我认为就是选在21-6与21-6*2之间的数字啊

楼上的NN 能否给翻译一下啊,偶看不懂啊 谢谢

cathyyan

musicbbt, where do you download the Math Prep? Can you please privide the link? Thanks!