Posted by **marissa** on Tuesday, October 6, 2009 at 8:44pm.

How many different four-digit numbers can you make from the digits 1,2,3, and 4 if each digit is used only once?

- 5th grade -
**Kelly**, Tuesday, October 6, 2009 at 9:07pm
1234

1324

1432

1243

1423

1342

2134

2143

2341

2314

2431

2413

3124

3142

3241

3214

3412

3421

4321

4312

4123

4132

4231

4213

24

there are 4 numbers...each can be used only once but 6 different ways

6x4=24

- 5th grade -
**Cliff**, Thursday, October 8, 2009 at 9:45am
This is a problem class known as permutations. There are 4 choices for your first number (i.e, 1,2,3,4)followed by 3 ways to pick the next number since there are only 3 numbers left. This leaves 2 ways to pick the next number and 1 way to pick the remaining number.

4*3*2*1 = 24

- 5th grade -
**David**, Sunday, January 22, 2012 at 11:55am
I am a 3-digit number.My first digit is a square number.My last digit is 3* my second digit,which is my half my first digit.What am I.

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