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Current time:0:00Total duration:2:18

Subtracting mixed numbers with like denominators

CCSS.Math: ,

Video transcript

- [Instructor] Let's say that we want to figure out what is seven and 11/12 minus one and 6/12. Pause this video and see if you can figure that out. All right now let's work on this together. So there's a couple of ways that you could approach this. You can view this as the same thing as seven plus 11/12 and then minus one and you might be tempted to say minus one and then plus 6/12 but remember you're subtracting not just the one you're subtracting one and you're subtracting 6/12 so minus one minus 6/12. Now why is that useful to think about it that way? Well now you can think about the whole numbers so you can say this is going to be seven minus one plus 11/12, plus 11/12 minus 6/12, minus 6/12. And so seven minus one is six, so it's going to be six plus now if I have 11 of something in this case 12ths and I'm subtracting six of them away six of the 12ths, I'm gonna be left with five of those somethings, five 12ths. So it's going to be six plus 5/12 which is the same thing as six and 5/12. Now as you get more used to this you could do some of this maybe even in your head, you could say hey look, look at the whole number parts, seven minus one is going to give me six and then if I say 11/12 minus 6/12 is going to give me 5/12 so that takes up a little bit less space. Another way that you might see this approached is you can rewrite this as seven and 11/12 minus, minus one and 6/12. Let me do the 6/12 in that blue color that I'm using for the fraction parts, 6/12 and then I would first focus on the fractional parts and I'd say 11/12 minus 6/12 is 5/12 and seven minus one is six and I got six and 5/12. So many different ways to approach the same thing and at the end of the day they really are the same underlying idea.