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Current time:0:00Total duration:5:02

CCSS.Math:

let's say we wanted to compute eight and thirty eight hundredths minus four and fifty four hundredths see if you can pause this video and figure it out on your own so there are multiple strategies for doing this I'll tell you the way that my head likes to do this I would view this as the same thing as eight and thirty eight hundredths and then I would subtract four and thirty eight hundredths the reason why I pick 38 hundreds is that will cancel out it'll take away these thirty eight hundredths and then I still have to subtract a little bit more if I already subtract 38 hundredths well I have to subtract a total of 54 hundredths so let's see 54 is how much more than 38 and I am doing this in my head as I speak let's see to go from 38 to 48 I need six I need ten more so I need to subtract another 16 I need to subtract another 1600s and how did I think about that well 54 is 38 and 16 so if I'm subtracting 54 I could break that up I could subtract 38 hundredths and then I could subtract 1600s why did I pick 38 hundreds because it matches up with this and so if I say 8 minus 4 is going to be 4 and then I have 38 hundredths minus thirty eight hundredths well those are just going to cancel out with each other so this minus that is just going to be 4 and then I say 4 minus 16 hundredths so how do we think about that well you might be able to do this in your head at this point you might say okay well I have to go 1600 s less than 4 that's going to be three and eighty four hundredths or you might want to just break it up you could say okay 4 is the same thing as 3 plus 3 plus 100 hundredths hundreds and then I want to take away minus sixteen hundred's well 100 minus 16 is 84 so this is going to be this here is 84 hundredths I'll write it out under its which I can write as zero point eight four and three plus zero point eight four well that's going to be this is going to be equal to we figured it out already multiple times three and eighty four three and eighty four hundredths now as I said there's multiple ways that we can try to tackle this for example another way that I could do this one right over here is I could say all right let me let me do the ones so let's say eight minus four eight minus four plus let me try to do the tenth so I could have three tenths minus five tenths 0.3 minus 0.5 and then I would have the hundredths so eight hundredths minus four hundredths so plus eight hundredths minus four hundredths now this is pretty easy to compute this is pretty easy to compute but what about this I don't have five tenths to take away well what I could do is instead of having an eight here I could take one away from it and make that a seven and so I have one that I can regroup someplace over here I can reorganize it so I could use two 7 plus 10 tenths and so I can take those ten tenths I could take those ten tenths and add them right over here so let me rewrite this I could rewrite this as 7 minus 4 plus 10 tenths plus 3/10 and I'm actually let me just write it all is plus 3/10 so I'm mixing different ways of writing it this way but that might be good minus five tenths and then this part I could just compute this is plus four hundredths plus 0.02 that color plus 4 hundredths this is right here is going to be 4 hundredths now what is this going to be 7 minus 4 is going to be 3 10 tenths plus 3 tenths just the right color so this is going to be 3 and then 10 tenths plus 3 tenths is 13 tenths minus 5 times is eight tenths and then I have four hundredths so once again three point eight four three ones eight tenths four hundredths or three and 84 hundredths