Perm and Comu formulas

[Dental2000]

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Look at #27 and #87 in the DAT Destroyer(2010 ed).

one uses n!/[r!x(n-r)!] while the other uses n!/(n - r)!

Could someone explain to me how to know which formula to use based on the questions wording????

 

[Tyrangiel]

I got a 23 in QR and I can't tell you... Not that you shouldn't try to find out haha

 

[spoog74]

Look at #27 and #87 in the DAT Destroyer(2010 ed).

one uses n!/[r!x(n-r)!] while the other uses n!/(n - r)!

Could someone explain to me how to know which formula to use based on the questions wording????

il try to hook u up but this is from what i know

Think of permutation use as ORDER MATTERS or an easier way to remember this is PERM or PERMANENT where ORDER MATTERS. This way, you wont ever forget to use the permutation rule of probability questions.

For combination remember order does not matter, think of it as a combination where you can make as many combos as possible and could care less.....


Thats the best i could do, as for WHEN to know to use it, practice would be helpful there.

Good luck

 

[rockclock]

I got a 23 in QR and I can't tell you... Not that you shouldn't try to find out haha

WOW. 😱

it boggles my mind how QR eludes pre-dents as a group...it is middle school and high school level math. i have a niece in the sixth grade that literally missed two questions on one of the topscore practice tests back when I was studying for the DAT...

OP: spoog has it right as far as the order matters/doesn't issue. if this were in-person tutoring I could go through and explain how you get those formulas but it's gonna be easy to get lost through a forum post. if all you care about is rote memorizing a formula and when to use it then spoog's explanation will be fine for the DAT.

 

[Dusk]

WOW. 😱

it boggles my mind how QR eludes pre-dents as a group...it is middle school and high school level math. i have a niece in the sixth grade that literally missed two questions on one of the topscore practice tests back when I was studying for the DAT...

OP: spoog has it right as far as the order matters/doesn't issue. if this were in-person tutoring I could go through and explain how you get those formulas but it's gonna be easy to get lost through a forum post. if all you care about is rote memorizing a formula and when to use it then spoog's explanation will be fine for the DAT.

well honestly, when's the last time you did all the math involved in the qr section? personally, I haven't done those since middle school... All my college physics and calculus classes really didn't prepare me for this level of math