Question

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

Answer 1

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

Answer 2

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

Answer 3

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.