This tutorial reviews how to use cancellation when multiplying fractions.
Examine the example 9/10 x 5/12.
Switching the numerators would not change the answer.
We can switch the 5 and 9.
Now we have the problem 5/10 x 9/12.
Both fractions can be reduced.
5/10 = 1/2 and 9/12 = 3/4
Multiply the reduced fractions together.
1/2 x 3/4 = 3/8
This is basically the same thing as using cancellation.