Estimating: Rounding Values Before Adding

Rounding values before adding is a great way to reach an estimation of your final value. The main purpose of estimating is to find a solution that is close to the actual solution but that you can find more quickly. For example, when adding 7,184 + 2,889 + 4,612 + 3,486, you can round the numbers to 7,200 + 2,900 + 4,600 + 3,500 and get the answer 18,200. Again, this is just an estimate of the actual sum of the original numbers. The actual sum would be 18,171.

Rounding Values before Adding

Rounding Values Before Adding

The main purpose of estimating is to find a solution that’s close to the actual solution but that you can find much more quickly. To demonstrate this, I’m going to solve this problem here twice, first by finding the actual solution and then secondly by estimating the solution. Let’s do that.

This problem describes some overstock inventory. There are four sections, and each section has a particular number of overstock units. We’re going to add all these up. We have first 7,184, 2,889, 4,612, and 3,486.

Now, we just need to add these up to get our total number of items in overstock. 4 plus 9 plus 2 plus 6 is 21. W have a 1 and we carry a 2. 2 plus 8 plus 8 plus 1 plus 8 is 27. We have a 7 here and we carry another 2. 2 plus 1 plus 8 plus 4 plus 6 is 21 again.

We’ll carry another 2. 2 plus 7 plus 2 plus 4 plus 3 is 18. We have 18,171 total units of overstock. Now, let’s solve this again by estimating these amounts. For each one, we’re going to round to the nearest hundred. For this one, we’ll take 7,200.

For this one, we’ll take 2,900. For this one, we’ll take 4,600. For this one, we’ll take 3,500. Now we can eliminate the adding of these first two columns, because they’re both zeros. Then, we just add up the remaining two. 2 plus 9 plus 6 plus 5 is 22. We’ll carry a 2. 2 plus 7 plus 2 plus 4 plus 3 is 18.

We were able to calculate this much more quickly. We have an error of 29 units, which is very small in comparison to the total. That is our estimation of the total number of units.

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by Mometrix Test Preparation | Last Updated: August 15, 2019