Luis has a simple calculator that has buttons for the digits 0 through 9, each of the 4 basic operations (+, - ,*,/ ), and an '=' button. Luis pushes a digit followed by the '+' sign, followed by another digit, followed by the '-' sign, followed by another digit and then the '=' sign. How many different answers could Luis get?
10 x 10 x 10 = 1000 possiblities, but they aren't all unique.
For example: 0 + 5+ 0 = 5
and 5 + 0 + 0 = 5 and 2 + 3 + 0 = 5
If you are looking for unique answers, the problem gets much harder.