Probability

[GRAD]

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What equations should we know for what- i havent done this stuff in like 10 years since grade school!

 

[_veo_]

basically prob = possible # of desired outcomes/ total # of possible outcomes

 

[GRAD]

yea but theres those factorial ones, when do you do n-1, when do you do n!/R!(n-r)!??? Stufflike that...

 

[_veo_]

The other one I know is, the number of different ways to arrange X number of things (given no repeats) is X!

 

[Dr. juju]

yea but theres those factorial ones, when do you do n-1, when do you do n!/R!(n-r)!??? Stufflike that...

The number of sequences (the order in which the items are selected matters here) of r items selected from n available items is

n!/(n-r)!


The number of groups (the order in which the items are selected does NOT matter here) of r items selected from n available items is

n!/(n-r)!r!

 

[lifeisgood]

(n-1)! is circular permutation formula

i.e. if you have 6 people, how many different ways can you seat them around a table?

(6-1)! = 5*4*3*2*1 = 120

 

[GRAD]

anything else? like how bout this one:

whats the prob of picking 3 black cards from a deck?

 

[GRAD]

when do you use n! by itself then?

 

[_veo_]

anything else? like how bout this one:

whats the prob of picking 3 black cards from a deck?

If you have a pack of 52 cards and you draw one card out, the
probability that it will be an black card is 26/52 because there are 26 black cards
in a deck of 52 cards. Now you will be down to 51 cards and 25 black cards, so if you draw a second card the probability that this one is also a black card is 25/51.. and so on

prob of picking 3 black cards from a deck = 26/52*25/51*24/50 = .118

 

[_veo_]

when do you use n! by itself then?

The factorial function is useful in computing the number of combinations that can be constructed from a set of objects.
Ex: you have 4 people, and you want to know how many ways they can stand in line. Then 4! = 24 ways

I don't think it is used for probability problems though. Sorry I mentioned it!

 

[GRAD]

thanks for the help =) hopefully ill figure all this out by next week=)

My dad's a math teacher and i think he'll prolly kill me if i get lower than a 18on QR