Concept

"Estimating" means making a smart guess about the answer. When we add numbers, sometimes it's easier to make a guess that's close enough instead of finding the exact number. We do this by "rounding" the numbers first, then adding them.

Rule

Rounding: This means making numbers simpler or "rounder." We change numbers to the nearest 10, 100, or another round number. Like turning 73 into 70.

Adding After Rounding: Once we round the numbers, we add these simpler numbers together. This gives us an estimate or a close guess of the total.

Example

Let's say we want to add 45 and 68.

Solution

That's a bit hard to do in our heads.
So, we round them first:

45 rounds up to 50,

and 68 rounds up to 70.

Now, we add the rounded numbers:

50 + 70 = 120.

So, 45 + 68 is about 120. That's our estimated sum!

Pre-requisite Skills

Before learning to estimate sums by rounding, you should know how to round numbers to the nearest 10 or 100. It's also important to be good at basic addition and understanding what numbers are closer to when rounded.