# Math Is Fun Forum

Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫  π  -¹ ² ³ °

You are not logged in.

## #1 2010-03-07 02:05:14

1a2b3c2212
Member
Registered: 2009-04-04
Posts: 419

### Combinations

A man goes to work by train, by taxi or by bus. In how many ways can he arrange his mode of travel for a 6-day week?

-What's the formula and the explanation?

Offline

## #2 2010-03-07 14:27:53

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Combinations

Hi;

If it is train or taxi or bus each day then we have:

3 choices the first day

3 choices the second day

all the way down to the 6th day

We use the multiplication rule: 3 * 3 * 3 * 3 * 3 * 3 = 3^6 = 9^3 = 729 ways

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Offline

## #3 2010-03-07 23:00:37

1a2b3c2212
Member
Registered: 2009-04-04
Posts: 419

### Re: Combinations

the multiplication rule is the permutation n^r rule right? so we have 3 modes to choose from and we are choosing 6?

http://www.mathsisfun.com/combinatorics/combinations-permutations.html

Offline

## #4 2010-03-08 09:34:27

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Combinations

Use n^r, 3 modes and you are choosing them 6 times. Because you have the same 3 choices over and over, you just multiply.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Offline