Four different sets of objects contain 2,5,6, and 7 objects, respectively. how many unique combinations can be formed by picking one object from each set?
a 114
b 400
c 420
d 20

There are 2 choices for the first set, and 5 choices for the second set. Each of the 2 choices from the first set can be combined with each of the 5 choices from the second set. Therefore there are 2 times 5 combinations from the first and second sets. Continuing this reasoning, the total number of unique combinations of one object from each set is:

No because if you do the higher number minus the lower number you will get a positive. if you do it the other way around you will get a negative number