>>Hi everybody,
>>
>>I've read a new puzzle and I can not figure this out, though my former colleague did it in seconds.
>>
>>Here it is:
>>
>>30 blind people participated in an experiment. In a closed room there were 5 drawers in 5 different colors. They were given 5 paper slips representing these colors and they have to match the colors.
>>It's known that all of them match at least one color.
>>10 matched only 1 color.
>>6 matched only 2.
>>4 matched only 3.
>>
>>The question is: how many matched exactly 4 colors and how many matched exactly 5.
>
>If 20 out of 30 matched less than four colors, then the remaining ten matched them all. Because you can't match only four - the fifth one has only place to go then.
>
>And the "all of them match at least one color" is there just to make sure there's nobody in the zero category.

Right. Simple, when you can think about it. But I didn't solve it myself, was thinking too hard.

Ok, here is another one:

There are 100 books on the table. Some opened, some closed. The first person comes into the room and closes open books and open closed. The second does the same, but with all even books. The third does it for each 3rd number, etc. 100 people came to the room. The quesiton is: how many open books would be on the table after all 100 people have been in the room?