Solving 3-digit addition in your head | 2nd grade | Khan Academy

TL;DR

Learn techniques for performing mental addition by manipulating numbers to make calculations simpler.

Transcript

• [Voiceover] What I want to do in this video is go over some techniques for doing mental addition. Now, if I saw something like 355 plus 480, if you have some paper around, you could write these numbers down and do your traditional addition, but you might want to be able to do these in your head, so how do you do it? Well, the way to think about i... Read More

Key Insights

• #️⃣ Mental addition involves manipulating numbers to make calculations simpler.
• 🍳 Breaking down numbers and rearranging the order of addition can simplify mental calculations.
• #️⃣ Adding or subtracting to make one number closer to a round number, like 500 or 700, helps in mental addition.
• #️⃣ Breaking down one number and adding parts of it to the other number is another technique for mental addition.
• 👻 Mental addition allows for quick calculations without the need for writing down numbers.
• ❓ Practice and familiarity with the techniques are essential for mastering mental addition.
• #️⃣ Manipulating numbers in mental addition requires logical thinking and number sense.

Questions & Answers

Q: How can mental addition be done without writing down the numbers?

Mental addition can be done by manipulating the numbers and simplifying them through addition or subtraction without needing to write them down. The key is to find ways to make the numbers more manageable.

Q: What is the purpose of breaking down numbers in mental addition?

Breaking down numbers allows for easier addition or subtraction. By breaking down a number like 355 into 335 and 20, it becomes simpler to add or subtract from other numbers, like 480 and 20, to perform mental calculations.

Q: What if the numbers in the addition problem are not easy to make simpler?

If the numbers in the addition problem are not easy to make rounder or simpler, other techniques like breaking down one number and adding parts of it to the other number can be used. This allows for easier mental calculation by manipulating the numbers.

Q: Is mental addition faster than traditional addition using paper?

Mental addition can be quicker than traditional addition using paper once the techniques and shortcuts are understood and practiced. It allows for faster calculations without the need for writing down numbers.

Summary & Key Takeaways

• Mental addition can be done by adding or subtracting from numbers to make them simpler.

• By breaking down numbers and rearranging the order of addition, calculations can be made easier.

• Techniques include adding or subtracting to make numbers rounder, like adding 20 to get to 500 or subtracting 4 to get to 700.