Video transcription

So how does one multiply fractions? Doesn't that sound difficult? Hi, I'm Jimmy Chang. I've been teaching College Math for nine years and even though we don't like fractions generally, multiplying fractions is actually one of the most straightforward things overall in Math that you can do. Now here's a couple of examples to illustrate that point. Suppose you have, 3/7 multiplied by 2/9. Now with multiplication by fractions, you literally just multiply across. Take the 3 and multiply it with the 2. "No kidding"; 3 times 2 is going to be 6; divided by 7 times 9 which, you know is 63. The only thing you may have to consider after you multiply fractions is reduce. Can you reduce 6/63? Well, at after some thought you'll see that 6/63 can both be divided by 3. As a result the, 6 divided by 3 is 2 and 63 divided by 3 is going to give you 21. Now sometimes you can save a little bit of trouble by multiplying fractions in a different way if you reduce ahead of time. Suppose you're multiplying 3/7 by 1/6. You can do what's called cross cancellation. In other words, if you're multiplying fractions, if one numerator can be reduced with one of the denominators; either or, you can cancel out and make the problem a little bit simpler. So for example, notice the 3 and the 6. They can both be divided by 3. So we're going to reduce both numbers by 3 right now; 3 divided by 3 is 1; 6 divided by 3 is 2. So what you're really doing is you're multiplying 1 times 1, 1 times 1 which i 1 and 7 times 2 which is 14 and no reduction is necessary. So, I'm Jimmy and there's some couple of strategies to help multiply fractions.