# Number- Using rounding numbers to find the sum and differences of numbers

Topic: Using rounding numbers to find estimated answersIf you need to refresh your mind on how to round numbers visit the previous topic, but for a quick summary if the number is greater than or equal to 5 we round up, otherwise we round down. Our aim today is to find the sum and differences of numbers by estimating and using the rounding numbers principles. Sometimes it is difficult to find the total or difference between two larger numbers, and that is where rounding makes it much easier.Finding the sumQuicklyestimate a sumby rounding each of theaddendsand adding them together. For example Estimate the sum of698and207. From first glance this look intimidating but take breath, you can handle this. You can easilyestimatea sum byroundingeach of the addends first!Remember: Roundingis making a number simpler but still keeping it close to what it was. When you round a number, first pick a target digit to round to. If the digit to the right of the target digit isless than 5,you rounddown. If the digit to the right of the target digit is5 or more,you roundup.Using the example above, let's round to thehundredsdigit. What's 698 rounded to the nearest hundred?(Remember to find the hundreds we look at the tens digit) if you guessed 700 then you are correct! What's 207 rounded to the nearest hundred? The answer is 200. Now you can easily add the rounded values. Using rounding, we see that the sum of698 and207 isabout900. The exact sum is not exactly 900, but close to that number. Example 2 Estimate the sum of415,67, and324. What's 415 rounded to the nearest hundred? That's right, 400 What's 67 rounded to the nearest ten? That's right, 70! What's 324 rounded to the nearest hundred? That's right, 300! Now you can estimate the sum by adding the rounded values! So, the sum of415,67, and324 isabout770. The answer isn't exact, but it's close. You congratulations can now use rounding to estimate sums! Finding the difference When you round the minuend and subtrahend in a subtraction equation, you make the subtraction simpler. You just have to remember to keep the differenceclose to the exact answer. Example Estimate923-486. Let's break the problem down to simple parts What's 923 rounded to the nearest hundred? 900 is the correct answer What's 486 rounded to the nearest hundred? 500 is the correct answer You can now easily subtract the rounded values! Hence, the difference of923 - 486isabout400. Example Estimate726 - 48. What's 726 rounded to the nearest hundred? 700 is the correct number What's 48 rounded to the nearest ten? 50 is the correct number You can estimate the difference by subtracting the rounded values. Hence, the difference of726 - 48isabout650.Tip:Notice that we alwayswrite the word "about"before the estimated difference.This tells us that the answer we got is not the exact answer, just an estimate.For a quick video lesson on today's topic watch the following video