180 of them.
500
There are 34 = 81 numbers.
27
pizza
There are 7,290 different 4-digit numbers that can be formed from the digits 1-9 without repetition.
There are 3024 of them.
180 of them.
There are 60480 numbers.
840
24
500
27 three digit numbers from the digits 3, 5, 7 including repetitions.
Oh, dude, let me break it down for you. So, you've got 5 digits to choose from for the hundreds place, then 4 left for the tens place after you've used one for the hundreds, and finally 3 left for the units place after using 2 for the hundreds and tens. Multiply those together and you get 60 possible 3-digit numbers. Easy peasy, lemon squeezy!
1 set
There are 5! = 120 such numbers.
There are 34 = 81 numbers.