## Thinking Mathematically (6th Edition)

The number of ways in which a series of successive things can occur is found by multiplying the number of ways in which each thing can occur. ------------ Applying the Principle on 12 different buns, 30 sauces, 4 types of lettuce, and 3 types of tomatoes. The total number of possible hamburgers is $12\times 30\times 4\times 3=4320$ hamburgers At 10 minutes each, the test would last for $43,200$ minutes $\quad...$ divide with 60 (min. per hour) = 720 hours $\quad...$ divide with 24 (hours per day) = 30 days