Estimating large sums

0:00- [Instructor] All right, we're asked to estimate 87,149 plus 12,227. And this little curly looking equals sign, that means approximately equal to, or what is this roughly equal to? So pause this video and have a go at this before we do this together. Alright, so I always like the problems with estimation, 'cause it means that I can kind of do things in my head, and there's not just one right answer.

0:25But when you have a multiple choice like this, you're just trying to find the answer that's closest to your estimation. So we have two numbers here, and they're both, they're both go all the way to the 10 thousands place. So I would feel good, we could either round this to the nearest 10,000 or we could round this to the nearest thousand if we want to get a little bit, a little bit more precise.

0:47I'm gonna round to the nearest thousand. So if we round this first number to the nearest thousand, what's it going to be? Well, it's closer to 87,000 than it is to 88,000. So I'll just call this 87,000, roughly speaking. And then 12,227, once again, if you run to the nearest thousand, it's closer to 12,000 than 13,000.

1:07So it's approximately or roughly going to be equal to 87,000 plus 12,000. Well, what's 87 plus 12? Well, 87 plus 12 is 99, so it's roughly equal to 99,000, which is exactly one of these choices right over here. And even if you got something a little bit different, like let's say that you wanted to round to the nearest 10,000.

1:32So then you would've had 90,000 here plus 10,000 here, you would've gotten it roughly equaling 100,000. Even then, 100,000 would've been closer to this last choice. Let's do another example. So pause the video and have a go at this one. Alright, now for this one, the first number is in the tens of thousands or it has a 10 thousands place.

1:55But this other number is much smaller. We only go to the hundreds place, so it doesn't make sense to round to the nearest thousand or round to the nearest 10,000. And so let's round just to the nearest hundred. So if we did that, this first number right over here, if we round to the nearest hundred, it's closer to 34,600 than it is to 34,700.

2:16So let's call this 34,600, roughly. And then the second number, if we round to the nearest hundred, it's closer to 200 than 100. So this is roughly going to be equal to 34,600 plus 200, which would be 34,600 plus 200 is 800, which is once again, exactly one of the choices here.

2:36But even if you rounded a little bit differently, you should probably still get a similar result. For example, even if you did round to the nearest thousand, which I wouldn't recommend, but if you did round to the nearest thousand, you would've gotten 35,000 here, and you would've gotten zero over here, 'cause zero, this is closer to zero than it is to 1,000.

2:55But then you would've said this is roughly equal to or approximately equal to 35,000, which is still much closer to choice B right over here than these other choices.