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Main content
Current time:0:00Total duration:3:09
CCSS.Math:

Video transcript

in this video we're going to get a little bit of practice estimating with multiplication so over here it says question mark is and then you have the squiggly equal sign and so you could view that squiggly equal sign as being what is this roughly equal to it doesn't have to be exactly right so what is roughly equal to 58 times six and so which of these choices would you pick pause the video and see if you can answer that so once again we don't have to get this exactly we just need to estimate what 58 times six is and the way that I would tackle it is hey can i rewrite 58 as a number that it's easy to multiply by six or easy to multiply in general and the easiest thing I can think of is 58 is awfully close to 60 so if you say that that is close to 60 if we're just estimating it well what would 60 times six be well 60 times six is the same thing as actually let me just write it this way you could view 60 times six as six times 10 times six which you could also view as six times six times ten and what's 6 times 6 that's 36 and then 36 times 10 is 360 so I would go with that choice right over there notice these other choices aren't even aren't anywhere close to that so we feel pretty good about our estimation let's do another example so here it's where I asked what's 3 times 2,890 what's that roughly equal to how would you estimate this pause the video and see if you can figure that out all right so 2,890 is not an easy thing to maybe multiply in our heads but I could say hey that's kind of close to 3,000 so I'm gonna say that this is going to be so it's going to be approximately equal to or roughly equal to 3 times 3,000 now what's 3 times 3 that's 9 so it's 3 times 3,000 well it's going to be 9 thousands and so it would be this choice right over there here's what I just did was a little bit confusing you could view 3 times 3000 as 3 times 3 times a thousand this part right over there is 3000 three times three is the nine and you have 9,000 9,000 let's do one more example this is going to involve fairly large numbers so what is if you have to estimate 5111 times nine which of these would you pick pause the video and answer that all right so I would view this this is roughly I would estimate it as 5,000 times nine and so 5,000 times nine that's the same thing as five times a thousand times nine which is the same thing as five times nine times a thousand five times nine is forty-five so it's gonna be 45 thousands or forty five thousand which is this choice right over there