(5 min)Review canceling

When you are drawing cards out of a deck, you may have noticed that
sometimes the denominator can get very big. You may find that it is
52 x 51 x 50 x 49 x 48 which is 311,875,200. Well this number might
be too big to fit into your calculator, so you might get an error.
Anyway, it is a nuisance to have such a big number and then try to
reduce it. An easier way to do it is to *cancel* like factors
in the numerator and denominator before you multiply, like
this:

This is the probability of drawing 3 spades in a
row

Remember that the factors you cancel don't need to be above each other in
the same fraction. In the above fraction, you see that the 4 in the
denominator of the first fraction can be canceled with the 4 in the
numerator of the second fraction. Try this:

3 5 11 18
--- x --- x ---- x ---- = ?
11 18 5 2