Estimating multi-digit addition and subtraction word problems | Grade 5 (TX TEKS) | Khan Academy

We're told Minley has 158,159 flight points. About how many total flight points does Minley have now? So why don't you pause this video and have a go at it? And remember, they don't want you to figure out the exact number; they just say about how many. So you just need to have a reasonable estimate.

All right, now let's work through this together. So, 2,118 flight points, if I were to round it to the nearest 10,000, that's going to be about 20,000 flight points. And then 158,159 thousand, I wouldn’t want to round it to the nearest 100,000 because then I'm rounding it at different levels. So if I round it to the nearest 10,000, then that is going to be approximately 160,000 flight points.

And then if I were to add those two numbers together, that means that Minley has about 180,000 frequent flyer miles or flight points. Let's do another example. So here they're telling us the Nile River is 6,650 kilm. The Tigers River is 1,950 kilm. I'm assuming kilometers long. About how many meters longer is the Nile than the Tigers River?

So pause this video and have a go at that. All right, let's work through this. So let's see, they both are in the thousands. So let's just round them both to the nearest thousand. The Nile River, if I were to round it to the nearest thousand, is approximately 7,000 kilometers. And the Tigas River, if I round it to the nearest thousand, is approximately 2,000 kilm.

So if I were to estimate this, I would say how much longer is the Nile than the Tiger? It would be 7,000 minus 2,000, which is approximately... well, that's 5,000. But I'm estimating the difference between these two numbers, which would be approximately 5,000 kilometers.