Using all digits from 0 to 9, allowing for repetition: a) How many different 3-digit numbers are possible? b) How many 3-digit numbers are possible in which there are no repeated digits? c) How many...

Using all digits from 0 to 9, allowing for repetition:

1. a) How many different 3-digit numbers are possible?

1. b) How many 3-digit numbers are possible in which there are no repeated digits?

1. c) How many 3-digit numbers are possible that contain at least one 5?