Lesson 5.1 · Adding and Subtracting Tens
10 more and 10 less
You know that a two-digit number is made of tens and ones. Now you can use that to find 10 more or 10 less in your head. No counting by ones needed!
Tens and ones
Look at the number 34. It has 3 tens and 4 ones.
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Each long row is a ten. The short row is the ones.
10 more
To find 10 more, add one more ten. Put one more long row in the picture. Now there are 4 tens and 4 ones. That is 44.
10 less
To find 10 less, take away one ten. Take away one long row. Now there are 2 tens and 4 ones. That is 24.
Only the tens digit changes
- 10 more: the tens digit goes up by 1.
- 10 less: the tens digit goes down by 1.
- The ones digit stays the same.
Worked example: 10 more than 52
52 has 5 tens and 2 ones. One more ten makes 6 tens. The ones stay 2.
10 more than 52 is 62.
Worked example: 10 less than 71
71 has 7 tens and 1 one. One less ten makes 6 tens. The ones stay 1.
10 less than 71 is 61.
Worked example: 10 less than 18
18 has 1 ten and 8 ones. Take away the ten. Now there are 0 tens and 8 ones.
10 less than 18 is 8.
Common mistake
Don't change the ones digit! 10 more than 45 is 55, not 46. Adding 1 changes the ones. Adding 10 changes the tens.
Tip
Count by tens starting at your number: 27, 37, 47, 57. Each jump is 10 more.
Practice
What is 10 more than 26?
Type a number.
What is 10 less than 59?
Type a number.
What is 10 more than 70?
Type a number.
What is 10 less than 13?
Type a number.
Mia has 85 stickers. She gets 10 more. How many stickers does she have now?
Type a number.
What is 10 more than 64?
Fill in the blank: 10 less than ___ is 30.
Type a number.
What is 10 more than 90?
Type a number.