You began your mathematical education adding, subtracting, multiplying, and dividing integers. From there you moved on to rational numbers, then to real numbers, and, perhaps, to complex numbers. But this is not the only kind of arithmetic mathematicians study. In fact, there’s a very different kind of arithmetic that you use every single day. The popular name for these calculations is clock arithmeticClock arithmetic, and it is indeed based upon the clock. Consider the following scenario: Suppose it is now 3:00 p.m., and you start on a 28-hour trip. What time will it be when you return? A quick calculation yields an answer of 7:00 p.m. How did you arrive at this answer? You did clock arithmetic. We will build carefully upon this idea, and we will apply many of the concepts we have already covered to help us understand it.