Consider these problems:(adsbygoogle = window.adsbygoogle || []).push({});

1. In how many ways can 7 boys be seated around a round table?

2. If seven beads of different colors are put on a ring how many different desighns can be made?

3. I have six books with identical black bindings, 8 with identical red bindings. In how many ways can I arrange them on a shelf so as to give the same apperance?

4. In how many ways can we choose a team of 5 from 10 boys?

Recently I've started to study probablity, the books I'm reading have a chapter on permutation and combination before the one on probablity.

Now the problem is that I think there are so many pitfalls in per & com problems.

For example in the first problem my answer was 7! but the book said that it's 7!/7.

In the second one I got 7!/7 (from what I learnt from the first one) and the right answer is 7!/7*2. In the third one I even didn't get the quetion and in the forth one my answer was (10C5) but the correct one was (10C5)/2 :yuck:

I can figure it out in two ways:

1. That's all a matter of experience and after solving some problems, I will do better.

2. In the next years of my study there are some mathematics that after learning them all the problems of per&comb will seem easy to me.

Which one is the case?

And the important question for me is:

Is understanding all of them necessary for learning probablity or I can loosen it up for now and get right into studying probablity?

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# Homework Help: Permutation and Combination

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