1. There
are 10, 000 combinations, you have 10 choices for the four digit and there are
10 x 10 x 10 x 10 which is 4-digit combination from 1-9. This is called combinations;
the calculation comes out to 10^4.
-50 - (-221) = 171
This is because subtracting a negative number is like adding a positive version of that instead. For a more simple example:
5 - (-2) = 7 or 5 + 2 = 7
13 R 1. Hope that helped!
