About this video
Sal multiplies 5/6 × 2/3 by multiplying the numerators and the denominators to get 10/18, then simplifies to 5/9 by dividing both by 2. He also shows you can divide out the common factor of 2 before multiplying and still get 5/9.
You'll be able to
- multiply two fractions by multiplying numerators and denominators.
- simplify a product to lowest terms.
- divide out a common factor before multiplying.
Key words
- numerator
- The top number of a fraction.
- denominator
- The bottom number of a fraction.
- common factor
- A number that divides evenly into two numbers, like 2 for 10 and 18.
- lowest terms
- A fraction where the top and bottom share no common factor except 1.
Transcript
We're asked to multiply 5/6 times 2/3 and then simplify our answer. So let's just multiply these two numbers. So we have 5/6 times 2/3. Now when you're multiplying fractions, it's actually a pretty straightforward process. The new numerator, or the numerator of the product, is just the product of the two numerators, or your new top number is a product of the other two top numbers.
So the numerator in our product is just 5 times 2. So it's equal to 5 times 2 over 6 times 3, which is equal to-- 5 times 2 is 10 and 6 times 3 is 18, so it's equal to 10/18. And you could view this as either 2/3 of 5/6 or 5/6 of 2/3, depending on how you want to think about it.
And this is the right answer. It is 10/18, but when you look at these two numbers, you immediately or you might immediately see that they share some common factors. They're both divisible by 2, so if we want it in lowest terms, we want to divide them both by 2.
So divide 10 by 2, divide 18 by 2, and you get 10 divided by 2 is 5, 18 divided by 2 is 9. Now, you could have essentially done this step earlier on. You could've done it actually before we did the multiplication. You could've done it over here. You could've said, well, I have a 2 in the numerator and I have something divisible by 2 into the denominator, so let me divide the numerator by 2, and this becomes a 1.
Let me divide the denominator by 2, and this becomes a 3. And then you have 5 times 1 is 5, and 3 times 3 is 9. So it's really the same thing we did right here. We just did it before we actually took the product. You could actually do it right here. So if you did it right over here, you'd say, well, look, 6 times 3 is eventually going to be the denominator.
5 times 2 is eventually going to be the numerator. So let's divide the numerator by 2, so this will become a 1. Let's divide the denominator by 2. This is divisible by 2, so that'll become a 3. And it'll become 5 times 1 is 5 and 3 times 3 is 9. So either way you do it, it'll work.
If you do it this way, you get to see the things factored out a little bit more, so it's usually easier to recognize what's divisible by what, or you could do it at the end and put things in lowest terms.
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