DAT tomorrow, please help with this Q:

[cougarblue84]

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I'm trying to put a few last minute formulas into the memory bank and Destroyer has me confused. On problem 20 in the solution it says "to calculate how many ways to order 'r' elements out of 'n' total elements use:

nPr = n!/(n-r)!"

Then, on problem 27, in the solution it says "to calculate how many ways to order 'r' elements out of 'n' total elements use:

nPr = n!/r!(n-r)!"

Which formula do you use?? Why does it give two different formulas using the exact same wording?

Help please...

 

[TheGreenWave]

I'm trying to put a few last minute formulas into the memory bank and Destroyer has me confused. On problem 20 in the solution it says "to calculate how many ways to order 'r' elements out of 'n' total elements use:

nPr = n!/(n-r)!"

Then, on problem 27, in the solution it says "to calculate how many ways to order 'r' elements out of 'n' total elements use:

nPr = n!/r!(n-r)!"

Which formula do you use?? Why does it give two different formulas using the exact same wording?

Help please...

The first equation is the correct one for PERMUTATIONS.
The second equation is the one for COMBINATIONS.

Just think of it this way in PERMUTATIONS order matters- when order matters there will be more possible outcome. So you want the equation thats dividing by less things. (thats how i remember at least)

To Summarize: permutations nPr = n!/(n-r)! AND combinations nCr = n!/r!(n-r)!


GOOD LUCK MAN!! Just relax if its possible and you will ace the DAT!!! 🙂

 

[cougarblue84]

Thanks for clarifying that for me! I'm crazy anxious about the test but I've put in a lot of study time so I really hope it pays off tomorrow. Thanks!

 

[MaChVa]

could you please show some simple examples of when you would use each of these equations and how to solve them?

 

[TheGreenWave]

could you please show some simple examples of when you would use each of these equations and how to solve them?

Well I dont feel like trying to come up with some straight off the top of my head. In the next few days I will likely do some math problems. If I find some that seem to be representative Ill post them and walk you through solving them.

Im frantically studying for the DAT which is in two and a half weeks so if I forget just pm me 🙂

 

[klutzy1987]

could you please show some simple examples of when you would use each of these equations and how to solve them?

If you would have a question how many ways can a comitee of a treasurer Vice president and president be made if selecting from 8 people then it would be 8!/(8-3)!

If it would ask ho many ways can 4 balls be selected from a bucket of 20 without replacement it would be 20!/((20-4)!4!)

 

[sl2obel2ts]

go watch a movie or something. chillaxxx

 

[TeamGuo]

good luck!!!!!!!!!!!!!!

 

[tsav23]

Cougarblue84,

Do you go to BYU?

 

[cougarblue84]

Yes sir. True blue through and through. You? Speaking of BYU -- I'll say it here first, watch for them as a possible BCS spoiler next season in college football. 🙂

 

[tsav23]

I would love to talk football, but I am sure that others on here would get bothered. I go to BYU as well.