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# Estimating decimal addition

CCSS.Math:

## Video transcript

what we're going to do in this video is get some practice estimating adding decimals so here it says twelve point nine three plus six point one is approximately equal to this little squiggly equal sign means approximately equal two so try to estimate this and pick the right choice so pause the video and try to do that all right now let's work through this together so we could work this out by hand but the whole goal here is estimation and so if I were doing this in my head I'd say well look twelve point nine three is a little bit less than thirteen and six point one is a little bit more than six and it's actually nice because when I rounded I went down on this number and I went up on this number so I went up seven hundreds to get to thirteen and I went down a tenth to get to six so I feel good when I add them up that we're gonna get pretty close to the actual answer so thirteen plus six is equal to 19 and lucky for us that that is one of the choices and there's multiple ways that you could try to estimate things for example you could do a little finer of an estimation you'd say this is approximately twelve point nine plus six point one and then you say twelve plus six is 18 and the 9/10 plus 1/10 is another one so you'd say this is eighteen plus one and you'd say okay that once again gets me pretty close to 19 or this gets me to nineteen let's do another example so here we're told five plus one plus four point nine one is approximately equal to what so pause this video and see if you can figure that out try to estimate it try to do it without any paper well the way I would do it is actually very similar to the way we just did the last one it's well five point one is approximately equal to five and it's approximately equal to five and four point nine one is also approximately equal to five I rounded to the nearest whole number in either case and so that would be equal to AK that would be equal to ten and once again it makes sense because we rounded down here and we rounded up here we rounded down to go from five point one to five and we round it up to go from four point nine one two-five if you're rounding down in both cases or rounding up in both cases it might get your estimate might get a little bit further from your actual answer so you might want to be a little bit careful all right so in this last example once again pause the video and see if you can work through it on your own well we're just going to do the same thing here this is going to be approximately equal to 3 plus I rounded down 3.14 rounded to the nearest whole number 3 5.9 to around it to the nearest whole number is 6 and once again just like I mentioned in the previous ones this is good because I'm rounding down from 3 point 1 4 to 3 I took away 1400s and then I add 8 hundredths to 5.92 so it's going to get me reasonably close to the actual answer and so 3 plus 6 is equal to 9 which is indeed one of the answers here and this is actually interesting you're not always gonna see a multiple choice so if you're trying to estimate things but in this case you know that just 3 plus 5 is going to be 8 and so this can't be the choice and then you're gonna have 8 plus whatever 14 hundredths plus 92 hundredths is and you know that's more than one so you know our answer is going to be a little bit over 9 so once again 9 is a good approximation