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# Estimating multi-digit multiplication

CCSS.Math:

## Video transcript

what I would like to do in this video is get some practice estimating the product of multi digit numbers and there's no better way of getting practice than just try and get ourselves and so right over here it says estimate when T nine times three thousand one hundred ninety eight why don't you pause this video and try to estimate this and of course you can do this by multiplying this out on paper or using a calculator but this is a useful skill try to do it in your head see if you can estimate what this is going to be well before even looking at these answers I would say this is going to be approximately equal to let's see 29 is awfully close to 30 and that I could multiply that times I could either multiply that times 3,200 which is awfully close to three thousand 198 or if I want an even more rough approximation I could say that's roughly equal to 30 times 3000 so if I did 30 times three thousand three times three is equal to nine and then I have one two three four zeros one two three four zeros and actually my approximation it turns out is here right over here at ninety thousand now if I wanted a slightly better approximation I could have said this is approximately equal to thirty times three thousand two hundred and this you could also do in your head you could say well what is three times thirty-two well that is going to be 96 and then you have one two three zeros one two three zero so this would be a slightly better approximation and if this is what you got the closest answer here is still going to be equal to ninety thousand let's do another example so here we are asked to estimate 137 times 18 so pause this video again and see if you can come up with an estimate try to do it in your head well--there's once again many ways of trying to tackle it the way I would tackle it I would say well that's pretty close to 140 times 20 and then this would be equal to 14 times 2 is 28 and then we have two zeros here so that would be roughly 2800 but when I look over here there is no 2800 and so maybe the closest one right over here is 2,000 so that would be my that could be an approximation another way it looks like she the way that they did it is they even did a course or approximation they rounded this to the nearest hundred and so they said this is approximately equal to one hundred times and they rounded this to the nearest ten 100 times 20 which is even easier to do in your head which is equal to two thousand which is this choice that they got right over here