How to Subtract Compound Fractions

Video Transcript

"Let's look at how to subtract compound fractions. A compound fraction is just another term for a mixed number. A lot of books use mixed number. And what that means is when you have a units part and then a fractional part as well. So this is called a mixed number. Mixed because it has a fraction and an integer part, or a whole number part also called a compound fraction. So if we want to subtract two and a quarter minus one and two ninths ok. What we would do is we need to turn both of these mixed numbers or compound fractions. We need to turn both of those into improper just meaning we need to turn the whole thing into a fraction. So we go like this. Four times two is eight plus one is nine fourths. So this mixed number as an improper fraction is nine fourths. Again the trick was this times that plus this is the top and the bottom stays. Minus nine times one is nine minus two is eleven ninths. Now those are not common terms, we don't have a common denominator there so we need to get a common denominator. The common denominator is going to be thirty six. So we need to say what do we need to multiply four by to get thirty six, and the answer is nine. So we do the same to the top, it gives me eighty one over thirty six. But do we need to multiply nine by to get thirty six, the answer is four, so we do the same on the top. It gives me forty four. So the final answer of this number minus that number, eighty one minus forty four is thirty seven over thirty six. Now that is an improper fraction. That means the top is bigger then the bottom, it means it's more then one represented as a fraction. So a lot of times teachers like to just simplify that. So we'll do that. If you take thirty six out of thirty six out of this it leaves you with one on top. So our final answer back in a mixed number form or compound fraction form is one and one thirty sixth."