5th grade
posted by marissa .
How many different fourdigit numbers can you make from the digits 1,2,3, and 4 if each digit is used only once?

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 
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 
I am a 3digit 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.