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Off Topic Test your maths abilities!

# Test your maths abilities!

13 replies
1

#### Test your maths abilities!

Silent_Control
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Hey guys, it's Sunday so it's time for maths!

Who can solve this simple problem?

In a class we have 30 students. We need to make a team, of 10 students, that can have maximum 4 girls. How many possibilities of picking there are, if we know that in the class there are 22 boys.

Good Luck!

EDIT: You don't need to give the exact result (unless you have a crazy computer). You can leave it in the final formula form.

#### Re: Test your maths abilities!

DoP3
User Offline

Nice trick into making us doing your homework..
but lol i'm bored so:
30 students>3 groups of 10
22 boys>8 girls 2 1
possiblities:
7 boys 3 girls
6 boys 4 girls
8 boys 2 girls
9 boys 1 girl
10 boys no girls

only 5 possibilties...
how simple can that be....
if this was your homework then lol what grade are you in?

#### Re: Test your maths abilities!

RAVENOUS
BANNED Offline

Class = 30 Students - 22 Boys and 8 Girls

10 boys - 0 girls
9 boys - 1 girl
8 boys - 2 girls
7 boys - 3 girls
6 boys - 4 girls

5 possibilities.

But that's not final

multiplicate the girls with the boys in the possibilities:

6x4 = 24
7x3 = 21
8x2 = 16
9x1 = 9
--------------------
10x0 = 1
--------------------
x = 71 possibilities.
Because only 10 Boys are also a group.

Lol. 6 minutes of thinking about.

#### Re: Test your maths abilities!

Silent_Control
User Offline

@ -Gas- : Dude, I've never had at Maths a mark lesser than a 10- , (A-) , so why do you think that I need your help to do homework.

Let's make it clear:

1) I do not have it for homework. I just found this problem and it seemed nice so I shared it with you.

2) I will post the response at the end of the day.

3) -GaS- and Skipper: Very wrong. It's not that easy.

Tip: Do not look at the solution like boys vs girls. Each person represents another choice. For example: we have 22 boys. We can consider them as an array B={b1,b2,...,b22}. We can also consider the girls as an array G={g1,g2,..,g8}. And we have to combine them.

Damn almost leaked the solution just to show you that it isn't for homework.

#### Re: Test your maths abilities!

DoP3
User Offline

In that case, skipper was right(in his second answer)

#### Re: Test your maths abilities!

Silent_Control
User Offline

Skipper, you're aproaching the correct answer.

#### Re: Test your maths abilities!

Tau
User Offline

There are 22 boys and 8 girls, huh? I guess we need the binomial coefficient to solve this one.

The answer should be:

(22 choose 10)
+ ((22 choose 9)*8 )
+ ((22 choose 8 )*(8 choose 2 ))
+ ((22 choose 7)*(8 choose 3 ))
+ ((22 choose 6)*(8 choose 4 ))

Too lazy to solve, but google says it's 28,352,940.

#### Re: Test your maths abilities!

Silent_Control
User Offline

We have a winner!

Yes, Thioester, you are right!

For those who don't understand, we have several cases.

Case 1:
0 girls. That means we have 10 boys that we have to choose from 22.

Case 2:

1 girl. We have 9 boys that we have to choose from 22. And we have 1 girl to choose out of 8. And because there will be 8 possibilites of choosing a girl it will result 8*(22 choose 9).

Case 3:

2 girls.

We choose 8 boys out of 22. We choose 2 girls out of 8.
This is (22 choose 8 )*(8 choose 2).

Case 4:

3 girls.

We choose 7 boys out of 22 and 3 girls out of 8.

Case 5:

4 girls.

We choose 6 boys out of 22 and 4 girls out of 8.

We sum the results of the 5 cases and this is the solution.

And "N choose K" is N!/(K!*(N-K)!), were N!=1*2*3*..*N and K!=1*2*3*...*K.

Again, good job Thioester!

#### Re: Test your maths abilities!

Cure Pikachu
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Wow. Around 28 million possiblities?! You must be kidding.
University A.Maths perhaps?

#### Re: Test your maths abilities!

Hazy
User Offline

Wow, I didn't think I could of solved this and yet I thought I was good at Maths,

Or maybe I'm just to lazy to try, lol

#### Re: Test your maths abilities!

Crazyx
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Ugh, I can'y understand half of what is written on this thread. I totally HATE Maths...

#### Re: Test your maths abilities!

DoP3
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Crazyx has written
Ugh, I can'y understand half of what is written on this thread. I totally HATE Maths...

you are gay if you hate maths. and you have no reason to live one this planet if you hate maths. You should die right now!

lol kidin
i didn't get muchc either, what class math is this?university or kindergarten ;P
can someone Xplain?

#### Re: Test your maths abilities!

Crazyx
User Offline

-GaS- has written
Crazyx has written
Ugh, I can'y understand half of what is written on this thread. I totally HATE Maths...

you are gay if you hate maths. and you have no reason to live one this planet if you hate maths. You should die right now!

lol kidin
i didn't get muchc either, what class math is this?university or kindergarten ;P
can someone Xplain?

You scared the hell out of me. LoL, I thought you were falming but I see you were just kidding.

#### Re: Test your maths abilities!

Silent_Control
User Offline

I think that it is for the 10th grade or something, because you learn the concept of "N choose K" in the 10th.
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