Adding within 100 and 10 more or 10 less (grade 1) · lesson

10 more and 10 less

💡 10 more or 10 less changes only the tens digit.

10 more than 34 is 44. Add one rod.

10 less than 58 is 48. Take one rod away.

🧠 How to think about it

Look at the tens digit. Go up one for 10 more. Go down one for 10 less. The ones stay put.

🏡 Try it at home

Start at 23. Take turns saying 10 more: 33, 43, 53. Then go back down.

💡 Add ones to ones. If you get 10 or more, make a new ten.

23 + 5: 3 ones and 5 ones are 8 ones. So 28.

46 + 7: 6 and 7 is 13. That is 1 ten and 3. So 53.

🧠 How to think about it

67 + 8: Get to the next ten first. 67 + 3 = 70. Then 5 more is 75.

🏡 Try it at home

Have 26 pennies in piles of 10 and 6. Add 7 more. Make a new pile of 10.

💡 Adding tens is like adding small numbers, but in tens.

30 + 20 is like 3 + 2. 3 tens and 2 tens are 5 tens, or 50.

52 + 30 adds 3 tens. 5 tens and 3 tens make 8 tens. 82.

🧠 How to think about it

Say it in tens: "5 tens plus 3 tens is 8 tens." Keep the 2 ones.

🏡 Try it at home

Use dimes as tens. Put out 3 dimes, then 2 more. How many cents?

💡 Taking away tens is like taking away small numbers, but in tens.

70 − 30 is like 7 − 3. 4 tens is 40.

90 − 60 is like 9 − 6. 3 tens is 30.

🧠 How to think about it

Cover the rods you take away. Count the rods that are left by tens.

🏡 Try it at home

Put out 8 dimes. Take away 5. How many cents are left?