Question

A bag contains 15 marbles numbered from 1 to 15. Two marbles are selected from the bag at the same time. Let event E = the two numbers do NOT differ by 10 How many outcomes are in the complement of E?

Answer 1

E is such that the numbers will not have difference of 10. We need to determine that the numbers picked randomly will have a difference of 10. Therefore there are 5 complements of E:
15 and 5
14 and 4
13 and 3
12 and 2
11 and 1