Chapter 3 - Probability - Exercises 3.1 - 3.34 - Applying the Concepts - Advanced - Page 123: 3.33e

There is one combinations in which no drug can be chosen There are 6 combinations in which 1 drug can be chosen There are 15 combinations in which 2 drugs can be chosen There are 20 combinations in which 3 drugs can be chosen There are 15 combinations in which 4 drugs can be chosen There are 6 combinations in which 5 drug can be chosen There is 1 combinations in which 6 drug can be chosen Adding all of them 0 + 1 + 6 + 15 + 20 + 15 + 6 + 1 = 64 total combinations

As given in answer