Math Destroyer Test #1, #40

[CaptainMadhater]

Could someone please explain this a little better, I don't exactly understand the formula for these types of question.

"In how many ways can 4 of the same physics books, 3 of the same algebra books, and 2 of the same chemistry books be arranged on a shelf?"

In the back of the book it says 9/(4x3x2) = (9x8x7x6x5x4)/(4x6x2) =1260

Where exactly did the 6 come from in the second part, in the denominator?

Thanks you guys

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[indigenoustw]

A useful thread here.

http://forums.studentdoctor.net/showthread.php?p=11378620#post11378620

You can look at my posts.
In short, a useful formula for this questions is this:

"The number of permutations possible out of n objects, (where p of one kind are alike, q of another kind are alike, ... and r of yet another kind are like) can be expressed as:

n!/(p! q!...r!) where p + q + ... + r = n "

So for your calculation, it would be 9!/(4!*3!*2!) = 1260

 

[CaptainMadhater]

Ok last week when you posted your reply i understood the formula for the permutations but i dont exactly understand how to apply it lol

For instance wtf is 9!

And where the hell did that 6 in the denominator come from lol

Thanks

 

[SEAirLand]

9! is simply 9 factorial.

This is 9x8x7x6x5x4x3x2x1 = 362,880