Addition within 100: Mental Strategies & Number Bonds
Free sample questions, a clear explanation, and 5 practice skills with an AI tutor that guides without giving the answer away.
Unlocking Your Addition Superpowers!
Hey Math Explorer! Have you ever built with LEGOs? Think of a small 1x1 brick as a "one" and a long 1x10 brick as a "ten." Adding numbers is just like putting your LEGO bricks together! Sometimes, you get enough small bricks (ones) to trade them in for a long brick (a ten). That's our big secret today!
Super Strategy 1: Make a Ten!
Our brains love the number 10! It's a friendly number that's easy to work with. When we add, we can be clever and make a ten first.
Let's try 8 + 6.
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How much does 8 need to become 10? It needs 2!
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We can split the 6 into a 2 and a 4 (that's a number bond!).
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Give the 2 to the 8. Now you have 10!
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Don't forget the 4! Now just do 10 + 4 = 14. Easy peasy!
This works for bigger numbers too! For 37 + 5, just give 3 from the 5 to the 37 to make 40. Then add the leftover 2. 40 + 2 = 42!
⭐ Key Takeaway!
To add faster, always look for ways to make a ten or add the tens and ones separately. It's like having a math shortcut!
Super Strategy 2: Sort and Stack!
When we add two 2-digit numbers, like 42 + 35, we can use a place value chart. It's like having special bins for our tens and ones bricks.
First, add the ones: 2 + 5 = 7. Then, add the tens: 4 tens + 3 tens = 7 tens. The answer is 77!
But what about 47 + 25? The ones (7 + 5) make 12! That's more than 9! Remember our LEGO trick? We regroup! We trade 10 of the "one" bricks for one "ten" brick. So, 12 ones becomes 1 ten and 2 ones. We move that new ten over to the tens column. Now we have 4 tens + 2 tens + our 1 new ten = 7 tens. Our answer is 7 tens and 2 ones, or 72!
Challenge Zone: Toy Store Tally!
You want to buy a bouncy ball for $36 and a kite for $28. No calculator allowed! How do you find the total cost with your brain power?
Here's one way: "I can take the tens first: 30 + 20 = 50. Then I'll add the ones: 6 + 8. I know 6+8 is 14. So, I just need to add 50 + 14. That's 64!" The total is $64! You did it!
Sample questions
Skills in this topic
- Add two 1-digit numbers mentally using number bonds.
- Add a 1-digit number to a 2-digit number mentally using number bonds and making a ten strategy.
- Add two 2-digit numbers without regrouping using place value charts.
- Add two 2-digit numbers with regrouping using concrete manipulatives (base-ten blocks).
- Explain how to quickly calculate the total cost of two items under $100 without a calculator, using mental math strategies.
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