Science NFT -Need math help

Frosty · 01-22-2009, 03:29 PM

Since it seems to be homework day on CP, I was hoping there were some math wizzes around. In the past, there were a few math majors around, IIRC.

My wife is helping out with the Math Is Cool team at our middle school and has run into a problem that she can't explain how to do mathematically. I am no help here because I sucked at probability in college.

The problem goes something like:"Cindy is buying four balloons. She can pick from any of four different colors. How many unique combinations can she make?"

On first thought, it would just be 4x4x4x4 (256). However, some of those combinations are duplicates (RRBB = RBBR). You can brute force it out by listing the different combinations to get the answer of 35 but this is too slow for a competition.

Any help on how to explain this mathematically so the kids can do the problem quickly?

rad · 01-22-2009, 03:37 PM

4x3x2x1=

tooge · 01-22-2009, 03:41 PM

The solution is this. Cindy is way to high maintenance to be involved with. She needs to decide on one freakin balloon color to make it easier. If she needs different ones, then get all 4 colors. Cindy probably asks for 3 different salad dressings all on the side too. She probably needs to have the lights off to have sex as well. Tell ya what. Keep away from this chick.

Frosty · 01-22-2009, 03:42 PM

Quote:

Originally Posted by rad

4x3x2x1=

Nope, because you can repeat colors.

The answer is 35, but I'm just not sure how to get it.

**Gonzo** · 01-22-2009, 03:43 PM

Are they filled with heroin?

It makes a difference.

**pr_capone** · 01-22-2009, 03:46 PM

My wife is a math geek. If you don't have an answer for this by the time she gets home I'll have her take a look at it.

TipRoast · 01-22-2009, 03:47 PM

Here's the equation you want:

(n+r-1)!
-----------
r! * (n-1)!

In your case,

n (number from which to choose) = 4
r (number chosen) = 4

So the equation reduces to this:

7!
-------
4! * 3!

or

7*6*5 * 4!
-----------
4! * 3!

which is 35.

**pr_capone** · 01-22-2009, 03:48 PM

well...

never mind then

**alpha_omega** · 01-22-2009, 03:48 PM

For sure not a math genius here, but wouldn't it be 4 to the 4th like your first thought?

**AustinChief** · 01-22-2009, 03:48 PM

(4+4-1)! / (4! * 3!) = 7! / 144 = 5040/144 = 35

**AustinChief** · 01-22-2009, 03:49 PM

Quote:

Originally Posted by TipRoast

Here's the equation you want:

(n+r-1)!
-----------
r! * (n-1)!

In your case,

n (number from which to choose) = 4
r (number chosen) = 4

So the equation reduces to this:

7!
-------
4! * 3!

or

7*6*5 * 4!
-----------
4! * 3!

which is 35.

Damn it.. beat me to it!

**alpha_omega** · 01-22-2009, 03:50 PM

Wow....you guys are smart.

I had a flashback to factorials as i was thinking about it, but i wasn't sure how it applied to this situation.

Frosty · 01-22-2009, 03:50 PM

Thanks, TipRoast!

bizzar54 · 01-22-2009, 03:50 PM

Beat me to it. Always get this confused with permutations and combinations.

Frosty · 01-22-2009, 03:52 PM

Quote:

Originally Posted by alpha_omega

Wow....you guys are smart.

I had a flashback to factorials as i was thinking about it, but i wasn't sure how it applied to this situation.

Me too. I went through a lot of high end math to get my engineering degree but I always had a brain lock on this stuff.

01-22-2009, 03:29 PM
Frosty Go Beavers! Join Date: Jan 2001 Location: Washington Casino cash: $3518243	NFT -Need math help Since it seems to be homework day on CP, I was hoping there were some math wizzes around. In the past, there were a few math majors around, IIRC. My wife is helping out with the Math Is Cool team at our middle school and has run into a problem that she can't explain how to do mathematically. I am no help here because I sucked at probability in college. The problem goes something like:"Cindy is buying four balloons. She can pick from any of four different colors. How many unique combinations can she make?" On first thought, it would just be 4x4x4x4 (256). However, some of those combinations are duplicates (RRBB = RBBR). You can brute force it out by listing the different combinations to get the answer of 35 but this is too slow for a competition. Any help on how to explain this mathematically so the kids can do the problem quickly?
Posts: 14,537

01-22-2009, 03:41 PM	#3
tooge MVP Join Date: Feb 2007 Location: Liberty, MO Casino cash: $804112	The solution is this. Cindy is way to high maintenance to be involved with. She needs to decide on one freakin balloon color to make it easier. If she needs different ones, then get all 4 colors. Cindy probably asks for 3 different salad dressings all on the side too. She probably needs to have the lights off to have sex as well. Tell ya what. Keep away from this chick.
Posts: 17,144

01-22-2009, 03:46 PM	#6
pr_capone THREEPEAT!!! Join Date: Jan 2006 Location: NWMO Casino cash: $9948214	My wife is a math geek. If you don't have an answer for this by the time she gets home I'll have her take a look at it.
Posts: 19,897

01-22-2009, 03:47 PM	#7
TipRoast Starter Join Date: Nov 2004 Casino cash: $9954900	Here's the equation you want: (n+r-1)! ----------- r! * (n-1)! In your case, n (number from which to choose) = 4 r (number chosen) = 4 So the equation reduces to this: 7! ------- 4! * 3! or 765 * 4! ----------- 4! * 3! which is 35.
Posts: 58

01-22-2009, 03:48 PM	#8
pr_capone THREEPEAT!!! Join Date: Jan 2006 Location: NWMO Casino cash: $9948214	well... never mind then
Posts: 19,897

01-22-2009, 03:48 PM	#9
alpha_omega Supporter Join Date: Jan 2004 Location: Liberty Casino cash: $-1560000	For sure not a math genius here, but wouldn't it be 4 to the 4th like your first thought?
Posts: 17,316

01-22-2009, 03:48 PM	#10
AustinChief Administrator Join Date: Aug 2000 Location: Austin Casino cash: $-514998	(4+4-1)! / (4! * 3!) = 7! / 144 = 5040/144 = 35
Posts: 19,997

01-22-2009, 03:50 PM	#12
alpha_omega Supporter Join Date: Jan 2004 Location: Liberty Casino cash: $-1560000	Wow....you guys are smart. I had a flashback to factorials as i was thinking about it, but i wasn't sure how it applied to this situation.
Posts: 17,316

01-22-2009, 03:50 PM	#14
bizzar54 Starter Join Date: Aug 2007 Location: Lees Summit Casino cash: $10004900	Beat me to it. Always get this confused with permutations and combinations.
Posts: 60