Estimating Differences

In the last lesson, you learned how to use rounding to estimate sums. π€

Do you know that you can also use rounding to estimate differences?

You can **estimate a difference** by rounding each number, then finding a difference that is **close **to the exact difference.

Here's a quick review on **rounding** rules.

If the digit one place to the right of the target digit isless than 5, you rounddown. π

If the digit one place to the right of the target digit is5 or more, you roundup. π

When you round the minuend and subtrahend in a subtraction equation, you make the subtraction simpler.

You just have to remember to keep the difference **close to the exact answer**. π

Let's look at this! π

Estimate923-486.

This is a pretty tough problem that would take several regroupings to solve.

Luckily for you, you can use **rounding** to **estimate** the difference! π€

**π€ Tip:** Unless otherwise stated, always round the numbers to the highest possible place value.

What's 923 rounded to the nearest hundred?

That's right, 900! π€

What's 486 rounded to the nearest hundred?

That's right, 500! π€

Now you can easily subtract the rounded values!

π So, the difference of **923 - 486 **is **about ****400.**

Let's try another example!

Estimate726 - 48.

What's 726 rounded to the nearest hundred?

That's right, 700! β

What's 48 rounded to the nearest ten?

That's right, 50! β

Now you can estimate the difference by subtracting the rounded values! π

π So, the difference of **726 - 48 **is **about ****650.**

You can now use rounding to estimate differences!

Great job! π

**Tip**: Notice that we always **write the word "about"** before the estimated difference. This tells us that the answer we got is not the exact answer, just an estimate.

Now, you can move on to practice. πͺ

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