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? :shrug:

4x3x2x1=

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.

Nope, because you can repeat colors.

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

Are they filled with heroin?

It makes a difference.

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.

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.

well...

never mind then :)

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

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

Damn it.. beat me to it!

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.

Thanks, TipRoast!

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

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.

You're welcome.

I happened to have a videotape of my last statistics class, right next to my videotape of the 2007 opening game versus the Jets. :D

I always wondered how many fellow engineers were on this site. Structural is my game.

Electrical here.

Well then I guess there is a good chance you make more than me...damnit!!!

Unlikely. I chose to work for a small company coming out of college so I could live in a small town in the sticks. I just got my first raise in almost 10 years and still make less than most new graduates do, despite almost 14 years experience. :grr:

Oh well, my house payment is $580 a month and it takes me 15 minutes to drive to work and I only work 40-45 hours a week (4 10s with Friday off) versus the typical 50 - 60 hours a week in the cities.

Mechanical.

Wow first raise in 10 years....they have some good year end bonuses? Hours are similar, although 5 - 9 hr days are no comparison to 4 - 11s. Although my house payment is double yours. Definitely something to be said about small town living.

Are you guys seeing the struggles of the economy with your companies. I never really thought too much of how shitty things were until friends emailed me asking for help getting a job. I know several KC firms that have laid off people. Always thought that engineering would be such a solid career. Guess it doesnt matter how great your company is if your clients just cant afford shit.

ROFL

I got a nice Carhartt jacket for Christmas?


Eh, I have a job that I like that isn't high pressure. :thumb:

Just eat lots of potatoes for me, okay?

Custodial