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# Estimating when subtracting large numbers

CCSS.Math:

## Video transcript

let's say that you have a jar of jellybeans and you know that there are exactly 282 jellybeans in that jar of jellybeans and then the next day you come and you see they're fewer and you say what happened and let's say someone who lives with you or your friend says oh yeah I did exactly and I ate 59 of those jellybeans so you started with 280 259 are taken out and you don't need to know exactly how many jellybeans are left but you want to estimate roughly how many jellybeans are left and that's why as this title of this video says we're going to estimate when subtracting large numbers and we can debate how large is large but these are reasonably large so let's do that let's see if we can estimate what 282 minus 59 is and sometimes when we're estimating we will use this squiggly equal sign this means approximately which is another just a fancy way of saying roughly what is this equal to so the way that I would approach this I would say hey are these close two numbers that are easier to subtract with so for example 282 I would say you know what maybe I can round to the nearest 10 here and so I could round it down to 280 if I rounded down to the nearest 10 if I round it up it would be go to 290 but 282 is closer to 280 than it is to 290 so I would round this when I'm estimating to 280 and then what about 59 if I were to round to the nearest 10 what would I round that to pause the video and think about that well 59 if I round down to the nearest tenth it would be 50 and if I round up to the nearest 10 it would be 60 and 59 is definitely closer to 60 so I would say that this is roughly if I'm rounding I could say hey I'm gonna round that to 60 so I could say that 282 minus 59 is roughly going to be 280 minus 60 and now what is this you might be able to do this in your head you could view this as 28 tens minus extends and so if you have 28 of something - 6 of it you're going to be left with 22 of that something and so you could say that this is going to be 22 tens 22 tens or another way to think about it you have two hundreds and then eight tens and then you're going to take six tens away from it so then you'll be left with two hundreds and two tens just like we have here so the whole point here this is not this is actually not exactly what 282 minus 59 is but if you just said hey ballpark do I you know I I want to know if do I have roughly how many jellybeans do I have well this this could be useful and you'll see later in life this is actually a very very useful skill where you might have these numbers that get a lot larger than this but you'll round to the nearest ten or you'll round to other places so that you can do that computation in your head