Thursday, May 17, 2007

Question of the Day

There are 18 topics in a full-unit course, and the professor will ask 10 questions in the exam. (We assume each question is about one topic and only one question can be asked on each topic.) I'm supposed to answer 3 of these questions.

How many topics should I study for to make sure that I have studied for at least 3 of the topics that appear on the exam?

I know it is solved by combinations, but I don't know how! Help me out!

See the comments for the answer :)


lightcapsule said...

So, my dad and my friend Baran agree on the following answer:

If you study 8 topics and the professor asks the other 10, you get a 0.

If you study 9 and the professor asks the other 9, you get 1.

You study 10, professor asks the other 8, you get 2.

The only way to make sure you get 3 is to study for 11 TOPICS!!! I'm going back to work.

pratsrandomwalk said...

yes 11 is the right answer. that's what i was about to put down - with the same logic. i mooted using a binomial distribution to figure out an answer, but you don't have an n and a p as a binomial would require.