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[futurebird]

My aunt says "I hate probability! Ask them this: How many ways can you take six blue marbles out of a bag with 12 blue marbles in it without replacement? Huh? How many!"

I was like ... um oneBut then she went off on me and said it was 362,880

Comments

[fox_hound]

I don't think the wording is good on this one.

To understand this better, you need to name each marbles. Marble1, marbel2, and so on until you have Marbel12.

Now take out Marble1 - 6. That would be one way. Now take out marble1-5 and 7. and keep on until you have marble1-5 and 12.

I think this would also include the order. So taking our marble 6 and going down until you have 1, would be different then going from 1 to 6.

I'm sure there is a math problem to get this number quickly, but I don't know it. I work more with logic.

[twinbee]

You can use permuations (since order matters). the formula for choosing k things from a group of n is [number of permuations of n things taken k at a time]

n!/(n-k)! = 12!/(12-6)! = 665280

I did that by hand on the back on an envelope, so it may be wrong.

If order does not matter, the problem might be worded "How many ways are there of choosing six blue marbles from a group of twelve, regardless of the order in which they are chosen."

Then we have [number of combinations of n things taken k at a time]

n!/k!(n-k)! = 12!/6!6! = 924

again I may be wrong bc of arithmatic error.

Here is a good resource on counting and elementary combinatorics: http://mathforum.org/dr.math/faq/faq.comb.perm.html

[anonymous]

This is what it's like to repeatedly hear from the same person you don't want to hear from.