Add & Subtract Multiples of 10 | 1st Grade Math

Add and Subtract Multiples of 10 - Grade 1 Math
Grade 1 Math  ›  Operations with Place Value  ›  Lesson 20
Grade 1 Math - Operations with Place Value

Add & Subtract Multiples of 10

Learn how to add and subtract multiples of 10 within 100 by thinking in groups of tens. Students use base-ten models, place-value reasoning, related facts, and mental math.

A problem such as 30 + 20 can be read as 3 tens + 2 tens, while 70 − 40 means 7 tens − 4 tens. Work with the tens first, then rename the result as a number.

Multiples of 10 Add tens Subtract tens Place value 1st Grade Math

๐ŸŽฏ What You Will Learn

Add groups of tens
Think of 30 + 20 as 3 tens + 2 tens.
Subtract groups of tens
Think of 70 − 40 as 7 tens − 4 tens.
Use place value mentally
Work with the tens without counting every one.
Use related facts
Connect 3 + 2 = 5 with 30 + 20 = 50 and related subtraction facts.
For parents & teachers — standards alignment: For addition, this lesson develops the place-value reasoning in CCSS 1.NBT.C.4, which explicitly includes adding a two-digit number and a multiple of 10; problems such as 30 + 20 are a special case of that expectation. For subtraction, the lesson directly addresses CCSS 1.NBT.C.6, which calls for subtracting multiples of 10 in the range 10–90 from multiples of 10 in the same range using models, drawings, place-value strategies, properties of operations, and the relationship between addition and subtraction. CCSS 1.NBT.C.5 also supports the 10-more/10-less reasoning used here. Texas Grade 1 TEKS 1.2(B) and 1.2(C) support the place-value models and representations. TEKS 1.3(A) specifically targets adding a multiple of 10 and a one-digit number, so the broader add/subtract-multiples-of-10 work in this lesson is additional Common Core-aligned practice for Texas students rather than a direct Grade 1 TEKS expectation.

๐Ÿง  Key Vocabulary

multiple of 10 — a number made from whole groups of ten, such as 20, 50, or 90.
ten — a group of 10 ones.
sum — the result of addition.
difference — the result of subtraction.
place value — the value a digit has because of its position.
related facts — addition and subtraction facts that use the same numbers or number relationships.

๐Ÿ”Ÿ Think in Groups of Ten

Multiples of 10 have 0 ones. That means you can often solve them by thinking only about how many tens you have.

30 + 20
3 tens + 2 tens = 5 tens
5 tens = 50
70 − 40
7 tens − 4 tens = 3 tens
3 tens = 30
Big idea: if 3 + 2 = 5, then 3 tens + 2 tens = 5 tens. The basic fact stays the same while the units are tens.

↕️ Ten More and Ten Less

10 more than 40 = 50
↔
10 less than 50 = 40

Adding or subtracting one ten changes the number of tens by 1. You do not need to count individual ones.

๐Ÿ› ️ Four Useful Strategies

Base-ten rodsBuild each amount with tens rods, then join or remove rods.
Think basic factsUse facts such as 4 + 3 = 7 to know 40 + 30 = 70.
Count by tensCount 10, 20, 30, 40... instead of counting ones.
Use related factsIf 30 + 50 = 80, then 80 − 50 = 30.
Common mistake: do not remove the zero and forget what the digits mean. You may use 7 − 4 = 3 to help with 70 − 40, but the answer is 3 tens, or 30—not 3.

๐ŸŒŸ 25 Worked Examples

Try each problem first. Then open “Show solution” to compare your tens strategy.
1 Add one ten
Find the sum: 20 + 10 = □.
Show solutionHide solution

20 is 2 tens and 10 is 1 ten. Two tens plus 1 ten makes 3 tens, so 20 + 10 = 30.

2 Match the cover addition
Find the sum: 30 + 20 = □.
Show solutionHide solution

Think in tens: 3 tens + 2 tens = 5 tens. Five tens is 50.

3 Add groups of tens
Find the sum: 40 + 30 = □.
Show solutionHide solution

Four tens plus 3 tens makes 7 tens. Therefore 40 + 30 = 70.

4 Add 2 tens to 5 tens
Find the sum: 50 + 20 = □.
Show solutionHide solution

5 tens + 2 tens = 7 tens, so 50 + 20 = 70.

5 Add to 90
Find the sum: 60 + 30 = □.
Show solutionHide solution

6 tens + 3 tens = 9 tens. Nine tens is 90.

6 Change the order
Find the sum: 10 + 70 = □.
Show solutionHide solution

Addition can be done in either order. Think 7 tens + 1 ten = 8 tens, so the sum is 80.

7 Use a double in tens
Find the sum: 40 + 40 = □.
Show solutionHide solution

4 tens + 4 tens = 8 tens. The sum is 80.

8 Combine 2 tens and 6 tens
Find the sum: 20 + 60 = □.
Show solutionHide solution

2 tens + 6 tens = 8 tens, so 20 + 60 = 80.

9 Make 100
Find the sum: 50 + 50 = □.
Show solutionHide solution

5 tens + 5 tens = 10 tens. Ten tens is 100.

10 Add to 90 another way
Find the sum: 70 + 20 = □.
Show solutionHide solution

7 tens + 2 tens = 9 tens. Therefore 70 + 20 = 90.

11 Subtract one ten
Find the difference: 80 − 10 = □.
Show solutionHide solution

8 tens − 1 ten = 7 tens. Seven tens is 70.

12 Match the cover subtraction
Find the difference: 70 − 40 = □.
Show solutionHide solution

7 tens − 4 tens = 3 tens, so 70 − 40 = 30.

13 Subtract 2 tens
Find the difference: 90 − 20 = □.
Show solutionHide solution

9 tens − 2 tens = 7 tens. The difference is 70.

14 Take 3 tens from 6 tens
Find the difference: 60 − 30 = □.
Show solutionHide solution

6 tens − 3 tens = 3 tens, so 60 − 30 = 30.

15 Subtract 2 tens from 5 tens
Find the difference: 50 − 20 = □.
Show solutionHide solution

5 tens − 2 tens = 3 tens. The difference is 30.

16 Take away one ten
Find the difference: 40 − 10 = □.
Show solutionHide solution

4 tens − 1 ten = 3 tens, so 40 − 10 = 30.

17 Subtract 5 tens
Find the difference: 80 − 50 = □.
Show solutionHide solution

8 tens − 5 tens = 3 tens. The answer is 30.

18 Subtract 6 tens
Find the difference: 90 − 60 = □.
Show solutionHide solution

9 tens − 6 tens = 3 tens. The difference is 30.

19 Subtract the whole amount
Find the difference: 70 − 70 = □.
Show solutionHide solution

7 tens − 7 tens = 0 tens. So 70 − 70 = 0.

20 Find what remains
Find the difference: 30 − 20 = □.
Show solutionHide solution

3 tens − 2 tens = 1 ten. One ten is 10.

21 Find a missing addend
Find the missing number: 30 + □ = 80.
Show solutionHide solution

Think in tens: 3 tens + how many tens = 8 tens? Five more tens are needed, so □ = 50.

22 Find the first addend
Find the missing number: □ + 10 = 50.
Show solutionHide solution

Think: how many tens plus 1 ten makes 5 tens? Four tens. So □ = 40.

23 Find the amount taken away
Find the missing number: 80 − □ = 20.
Show solutionHide solution

Think: 8 tens minus how many tens leaves 2 tens? Six tens, so □ = 60.

24 Find the starting amount
Find the missing number: □ − 40 = 20.
Show solutionHide solution

The starting amount must be 4 tens more than 2 tens. 2 tens + 4 tens = 6 tens, so □ = 60.

25 Use related addition and subtraction
Use 10 + 80 = 90 to solve 90 − 80.
Show solutionHide solution

Because 1 ten + 8 tens = 9 tens, the related subtraction fact is 9 tens − 8 tens = 1 ten. So 90 − 80 = 10.

๐ŸŽฎ Independent Practice — 30 Problems

  1. Find the sum: 10 + 20 = □.
  2. Find the sum: 20 + 30 = □.
  3. Find the sum: 30 + 40 = □.
  4. Find the sum: 10 + 50 = □.
  5. Find the sum: 20 + 70 = □.
  6. Find the sum: 30 + 60 = □.
  7. Find the sum: 40 + 50 = □.
  8. Find the sum: 10 + 90 = □.
  9. Find the sum: 20 + 80 = □.
  10. Find the sum: 40 + 60 = □.
  11. Find the difference: 90 − 10 = □.
  12. Find the difference: 80 − 20 = □.
  13. Find the difference: 70 − 30 = □.
  14. Find the difference: 60 − 20 = □.
  15. Find the difference: 50 − 30 = □.
  16. Find the difference: 40 − 20 = □.
  17. Find the difference: 90 − 30 = □.
  18. Find the difference: 80 − 40 = □.
  19. Find the difference: 70 − 50 = □.
  20. Find the difference: 60 − 50 = □.
  21. Find the missing number: 20 + □ = 60.
  22. Find the missing number: □ + 10 = 50.
  23. Find the missing number: 90 − □ = 40.
  24. Find the missing number: □ − 20 = 50.
  25. Which is 10 more than 60: 50, 60, or 70?
  26. Which is 10 less than 40: 20, 30, or 50?
  27. Write an addition equation with two multiples of 10 that has a sum of 100.
  28. Write a subtraction equation with two multiples of 10 that has a difference of 20.
  29. Solve 30 + 50 and explain the answer in tens.
  30. Solve 90 − 40 and explain the answer in tens.

๐Ÿ† Lesson Test — 15 Questions

  1. Find the sum: 10 + 10 = □.
  2. Find the sum: 10 + 30 = □.
  3. Find the sum: 10 + 60 = □.
  4. Find the sum: 20 + 20 = □.
  5. Find the sum: 30 + 30 = □.
  6. Find the difference: 80 − 30 = □.
  7. Find the difference: 90 − 70 = □.
  8. Find the difference: 70 − 10 = □.
  9. Find the difference: 50 − 10 = □.
  10. Find the difference: 80 − 70 = □.
  11. Find the missing number: 30 + □ = 100.
  12. Find the missing number: 60 − □ = 50.
  13. Find the missing number: □ − 60 = 10.
  14. Find the missing number: □ − 40 = 10.
  15. Explain why 40 − 30 = 10 using tens.

๐Ÿ” Complete Answer Key

Show practice answer keyHide practice answer key

Practice Answers

1. 30
2. 50
3. 70
4. 60
5. 90
6. 90
7. 90
8. 100
9. 100
10. 100
11. 80
12. 60
13. 40
14. 40
15. 20
16. 20
17. 60
18. 40
19. 20
20. 10
21. 40
22. 40
23. 50
24. 70
25. 70
26. 30
27. Possible answer: 40 + 60 = 100.
28. Possible answer: 70 − 50 = 20.
29. 80. Three tens + 5 tens = 8 tens.
30. 50. Nine tens − 4 tens = 5 tens.
Show test answer keyHide test answer key

Test Answers

1. 20
2. 40
3. 70
4. 40
5. 60
6. 50
7. 20
8. 60
9. 40
10. 10
11. 70
12. 10
13. 70
14. 50
15. 40 is 4 tens and 30 is 3 tens. Four tens − 3 tens = 1 ten, and 1 ten is 10.

๐Ÿ’ก Common Mistakes to Watch For

Giving a ones answer instead of a tens answer
7 − 4 = 3 helps with 70 − 40, but 3 tens means 30.
Counting every one
Use groups of 10 and place value instead of recounting 50 or 80 objects one by one.
Switching subtraction order
70 − 40 is not the same as 40 − 70.
Forgetting related facts
Addition can help you check subtraction, and subtraction can help you check addition.
What comes next: Lesson 21 begins Unit 4 with Compare and Order Lengths.

๐Ÿ”— Related Lessons

Lesson 18 — Add Within 100 Using Tens and Ones Review the place-value reasoning behind addition within 100. Lesson 19 — Add a Two-Digit Number and a One-Digit Number Review how the ones place and new tens affect addition within 100.

๐Ÿ–จ️ Printable Companion

A future Add & Subtract Multiples of 10 Practice Pack can include base-ten models, add-the-tens practice, subtract-the-tens practice, missing-number equations, 10-more/10-less activities, mixed review, and a complete answer key.

← Lesson 19: Add a Two-Digit Number and a One-Digit Number Grade 1 Math Hub Next: Compare and Order Lengths →

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