How many 3-digit numbers are made up entirely of odd digits?

Another way of asking the question: How many different 3-digit arrangements can be
done using the digits 1,3,5,7,9 - if each digit can be repeated?

First digit (100's) can be filled in 5 ways
10's digit can also be filled in 5 ways.
Units digit can also be filled in 5 ways.

So the total number of arrangements possible (or the number of 3 digit numbers
with only odd digits) = 5*5*5 = 125.

Hope you got it. Let me know if it is not clear :)