If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:3:34

Estimating division that results in non-whole numbers

CCSS.Math:

Video transcript

so let's think about something a little bit what do you think 17 divided by 2 is going to be well you might immediately realize that it's not obvious what you need to multiply 2 by in order to get to 17 there's no whole number that I could put here that gets us to 17 we know that 2 times let's see 2 times 8 is a little bit less than that 2 times 8 is equal to 16 and we know that 2 times 9 is going to be a little bit more than that is equal to 18 and so this question mark 2 times question mark is equal to 17 this helps us know that our question mark our unknown value here is going to be between 8 & 9 it is going to be 8 point something so let's do another example if someone were to ask you hey let's think about 18 divided by 4 and you don't have to figure out exactly what it is just yet but I want you to think about what two consecutive whole numbers is 18 divided by 4 whatever that is what is that between well we could do something similar we could say all right let's see 4 times 4 is equal to 16 so that doesn't quite get us to 18 we could say that 4 times 5 is equal to 20 so that's more than 18 so 4 times question mark is equal to 18 this helps us realize that because 18 is between 16 and 20 this question mark right over here is going to be between 4 & 5 so 18 divided by 4 is going to be 4 point something now another way of thinking about or estimating what division might result in is through an inequality so if I were to say 87 divided by 9 how would you compare that to 10 over here so there's a couple of ways you could compare it you could say maybe this is greater than 10 maybe it's equal to 10 maybe it is less than ten so pause this video and see if you can figure that out what would you put here is it less than greater than or equal to ten well we know it's not equal to ten we know that ninety divided by nine is equal to ten and let's see if we go one multiple of nine less than that we know that 81 divided by nine is equal to nine and so 87 divided by nine is in between these two values let me do this in another color so 87 divided by nine is going to be something in between nine and ten and so it is going to be less than ten so the whole point of this video is start to get us a little bit comfortable with this idea of dividing where we might get an answer that is not a whole number and in the future we'll learn how to compute that but for now we're just learning to estimate and just get a sense of hey okay this is going to be between eight and nine this is going to be between four and five this is going to be between nine and ten which just means it's going to be nine point something which means it's going to be less than ten