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Introduction:

In order to estimate sums and differences, you first need to learn the key points. The key points are really the definitions and steps to estimating the sum or the difference between two numbers. Let's get started!

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Key Points:

The key points to estimating sums and differences are:

- Estimating means to make an educated and approximate calculation; not exact
- Sum is the answer to an addition problem
- Difference is the answer to a subtraction problem
- When the digit is below 5, 50, 500, etc. you will estimate below that value
- When the digit is above 5, 50, 500, etc. you will estimate above that value

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Examples:

Now that you have been introduced to the topic and its key points, let's take a look at an example to understand it better!

__Estimate the __*sum* of 48 and 103

Keep in mind that sum means the answer to an addition problem. Therefore,we must add the following numbers: 48+103. Now, you also must remember not to directly add the numbers. The key point is estimate. So, let's see how we can answer this problem using a very easy method!

First, we will look at the last digit of the first number: 48. Since 8 is greater than 5, we must round up to 10. Therefore, now we have 50+103. But remember that we must round __both__ numbers to get our estimate. Since 3 is less than 5, we will round that to 0, so it will become 50+100, which equals 150. That means that the estimate for 48+103 equals 150!

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Checking...

It's a good idea to check your answer by finding the direct answer and then determining whether your estimate is reasonable or not. To do that, you just simply add the original problem: 48+103, which will give you an answer of 151. Now, ask yourself, " Is my estimate reasonable, according to the actual answer?"

Well, our estimate is reasonable because 151 is only 1 digit away from 150. Easy, right?!

*Sheet 1 How to Estimate Sums*

*Sheet 2 How to Estimate Differences*