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3rd grade (U.S.)

3rd grade is full of some of the most important ideas in mathematics. You'll extend the addition and subtraction that you did in second grade to more than two digits. You will also get your first exposure to the ideas of multiplication, division, and fractions, which will be used the rest of your mathematical lives (we'll even use some letters as placeholders for unknown numbers along the way). 3rd grade is also when we first think about area (how much "space" something takes on a surface) and perimeter (the distance around a shape). All of that will be rounded out by making sure that you can apply these ideas in the real world and see patterns in the mathematical world. (Content was selected for this grade level based on a typical curriculum in the United States.)
Community Questions
Addition and subtraction
In the 2nd grade you learned to add and subtract 2-digit numbers. Now we take things further by adding and subtracting three-digit numbers. This is good practice for 4th grade where you'll be expected to add or subtract pretty much any whole number!
All content in “Addition and subtraction”

Adding with regrouping within 1000

You're somewhat familar with adding, say, 17 + 12 or 21 + 32, but what happens for 13 + 19? Essentially, what happens when I max out the "ones place"? In this tutorial, we'll introduce you to the powerful tool of regrouping and why it works. Common Core Standard: 3.NBT.A.2

Using regrouping to subtract within 1000

You can subtract 21 from 45, but are a bit perplexed trying to subtract 26 from 45 (how do you subtract the 6 in 26 from the 5 in 45). This tutorial is your answer. You'll see that we can essentially "regroup" the value in a number from one place to another to solve your problem. This is also often called borrowing (although it is like "borrowing" sugar from your neighbor in that you never give it back). Common Core Standard: 3.NBT.A.2