Adding and subtracting within 100 (grade 2) · lesson

Facts you know by heart

💡 Knowing small facts fast makes big problems easier.

8 + 7 is a near double. 7 + 7 = 14, so 8 + 7 = 15.

14 − 6? Think 6 + 8 = 14. So the answer is 8.

🧠 How to think about it

If you don't know a fact, use one you do know. Doubles and make-ten facts help.

🏡 Try it at home

Play a quick game. Say a fact like 9 + 6. Your child answers fast. Swap turns.

💡 When the ones make 10 or more, trade 10 ones for a new ten.

47 + 38. The ones are 7 + 8 = 15. Write 5 and carry 1 ten.

The tens are 4 + 3 + 1 = 8. The answer is 85.

🧠 How to think about it

Add the ones first. If you get 10 or more, carry a ten. Then add the tens, plus the carried one.

🏡 Try it at home

Use dimes and pennies. Show 47¢ and 38¢. Trade 10 pennies for a dime. How much?

💡 If there aren't enough ones, trade a ten for 10 ones first.

63 − 28. You can't take 8 from 3. Trade a ten. Now 13 − 8 = 5.

There are 5 tens left. 5 − 2 = 3. The answer is 35.

🧠 How to think about it

Never flip it to 8 − 3. Trade a ten instead. Then take away the ones, then the tens.

🏡 Try it at home

Show 52¢ with dimes and pennies. Pay 17¢. Trade a dime for 10 pennies when needed.

💡 To add a list, add all the tens, then all the ones.

12 + 25 + 30. Tens: 10 + 20 + 30 = 60. Ones: 2 + 5 = 7.

60 + 7 = 67.

🧠 How to think about it

Write the tens in one list and the ones in another. Add each list. Then put them together.

🏡 Try it at home

Add up the prices on three small items from a store ad. Add tens, then ones.

💡 Good tricks break numbers apart in ways that keep the total the same.

38 + 5 = 38 + 2 + 3. You make 40, then add 3. That is 43.

56 − 19: take 20, then add 1 back. You took 1 too many.

🧠 How to think about it

Ask what the trick did. Did it split by tens and ones? Make a ten? Take a round number and fix it?

🏡 Try it at home

Ask your child to solve 29 + 6 two ways. Talk about which way was easier.