11th OG 71题

albertjerrys

71. A number of people each wrote down one of the first 30 positive integers. Were any of the integers written down by more than one of the people?

(1) The number of people who wrote down an integer was greater than 40

(2) The number of people who wrote down an integer was less than 70

Key is A.

有点看不懂这道题的意思。好像是说一群人每个人写下一个30以前的正整数。有没有数字被谢过超过一次。

（1）这群人写下的整数有一个大于40，但是不是说first 30吗？怎么会又有40？

hjgjfgfb

each person writes down one number range from 1 to 30, then the question asks whether all the 30 numbers are repeated.

(1) is sufficient, for all the 30 number to be repeated once, at least 60 people are needed.

(2) is not sufficient, although there are 70 people writing down the numbers, it's not necessary that all the 30 numbers are included and repeated.

albertjerrys

楼上的，先谢过了。

请问如果至少需要60人才有可能把1-30个数字都写两次，但是（1）只说了这群人数是大于40的，但是没有说一定是大于60呀？

angelavivi

QUOTE:

71. A number of people each wrote down one of the first 30 positive integers. Were any of the integers written down by more than one of the people?

(1) The number of people who wrote down an integer was greater than 40

(2) The number of people who wrote down an integer was less than 70

Key is A.

有点看不懂这道题的意思。好像是说一群人每个人写下一个30以前的正整数。有没有数字被谢过超过一次。

（1）这群人写下的整数有一个大于40，但是不是说first 30吗？怎么会又有40？

呃……这题是这样的，题目是问是否有任何一个数字有被写到两次的可能，所以说，只要有31个人来参加这个写数字的活动，就至少会有一个数字被写两次

条件1的意思是，写数字的人数大于40，40>31，显然答案是A

不知道我解释清楚没有？

qiuqiaomm

Agreed!

Pls ignore my previous explanation. it's totally nonsense