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

Subtracting mixed numbers with like denominators

CCSS.Math: ,

Video transcript

let's say that we want to figure out what is seven and eleven twelve minus one and six twelve pause this video and see if you can figure that out alright 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 7 plus 11 12 and then minus one and you might be sent tempted to say minus 1 and then plus 6 12 but remember you're subtracting not just the one you're subtracting 1 and you're subtracting 6 12 so minus 1 minus 6 12 now why is that useful to think about it that way well now you can think about the whole number so you could say this is going to be 7 minus 1 plus 11 12 plus 11 12 minus 6 12 minus 6 twelfths and so 7 minus 1 is 6 so it's going to be 6 plus now if I have 11 of something in this case 12 and I'm subtracting 6 of them away 6 of the 12 I'm going to be left with 5 of those something's 5 twelfths so it's going to be 6 plus 512 which is the same thing as 6 and 512 now as you get more used to this you could do some of this maybe even in your head you can say hey look look at the whole number parts 7 minus 1 is going to give me 6 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 could rewrite this as 7 and 11 12 minus minus 1 and 6 12 let me do the six twelfths 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 so minus 6 12 is 512 and 7 minus 1 is 6 and I got 6 and 5 twelfths so many different ways to approach the same thing and at the end of there really are the same underlying idea