7-25-08 数学

mitboy88UID: 2506960

can any one please show me how to solve the folloing problems? thanks!!

1. Given that 500 people are asked 2 questions and both questions canbe answered either yes or no. If 410 said yes for first and 220 saidyes for second, then how many answered both?

2. For a party, 2 types of dishes are to beselected. For the first type of dish 2 are to be selected from 4 andfor second type of dish 4 are to be selected from 5. In how many wayscan these both(1st & 2nd) type of dishes selected?

[ 本帖最后由 Adamas 于 2009-1-4 03:21 编辑 ]

emily-2008UID: 2458445

Let me try

1.  between 130 and 220

2. 30

GRE729UID: 2509967

1。 130
410+220—500=130
2    30

emily-2008UID: 2458445

look, it is not a question about set.
In my opinion, the 220 people who said yes can also belong to the 410 people who said yes for the first.
Another possiblity is that the first time 90 saying no people are included in the 220 people.
So I think the number should between 130 and 220

GRE729UID: 2509967

恩，对。应该 是130-220之间，谢谢