Solved Exercises on Subtraction Within 20 in Grade 1

Master subtraction within 20: basic facts, visual representation, and problem solving through these 5 detailed exercises.

Solution: Exercises 1 to 3
1 Basic Subtraction Facts
Exercise 1
Solve: 13 - 5 = ?
Definition:

Subtraction: Taking away one number from another

Basic Facts: Subtraction problems with numbers from 0 to 20

Within 20: Problems where the minuend is 20 or less

Counting Back Method:
  1. Start with the first number (13)
  2. Count backward the second number of steps (5 steps back)
  3. Land on the final number which is the answer
  4. Write the complete equation
8
9
10
11
12
13
14
15
16
Jump 1
Jump 2
Jump 3
Jump 4
Jump 5
Step 1: Start with the first number

Start counting at 13

Step 2: Count backward 5 more numbers

Count: 12, 11, 10, 9, 8

Step 3: Land on the answer

We land on 8

Step 4: Write the equation

13 - 5 = 8

13 - 5 = 8
Final answer:

13 - 5 = 8

Applied rules:

• Counting backward: Subtracting means moving to smaller numbers

• Sequential counting: Count one number at a time backward

• Final position: The last number reached is the difference

2 Number Bonds
Exercise 2
Show how 15 can be broken down: 15 - ? = 7
Definition:

Number Bond: Shows how a number can be split into parts

Part-Whole Relationship: Smaller numbers that combine to make a larger number

15
8
7
Step 1: Identify the whole number

We start with 15 (the whole)

Step 2: Identify the remaining part

After subtraction, we have 7 left

Step 3: Find the missing part

Count down from 15 to 7: 15, 14, 13, 12, 11, 10, 9, 8

We counted 8 numbers down, so the missing part is 8

Step 4: Verify the bond

8 + 7 = 15 ✓

15 - 8 = 7
Final answer:

15 - 8 = 7, so the missing number is 8

Applied rules:

• Number bonds: Help understand how numbers break apart

• Counting down: Start with the whole and count to the part

• Verification: Check that the parts add up to the whole

3 Ten Frame Subtraction
Exercise 3
Solve: 12 - 4 = ? using ten frames
Definition:

Ten Frame: A visual tool with 10 boxes to show numbers

Visual Learning: Using pictures to understand numbers

1
2
3
4
5
6
7
8
9
10
11
12
Step 1: Show the first number

Fill 12 boxes (first 10 and 2 more)

Step 2: Cross out the second number

Cross out 4 boxes: 12, 11, 10, 9

Step 3: Count remaining

Boxes left: 8

Step 4: Count total

First frame: 6 remaining, Second frame: 2 remaining, Total: 8

12 - 4 = 8
Final answer:

12 - 4 = 8

Applied rules:

• Ten frame strategy: Using groups of 10 makes subtraction easier

• Visual grouping: Seeing numbers in groups of 10

• Sequential counting: Counting by tens and ones

Rules and methods, laws,...
\(13 - 5 = 8\)
Subtraction Within 20
Subtraction
Property
Not commutative
Identity
Property
n - 0 = n
Zero
Rule
Subtracting 0 changes nothing
Key definitions:

Subtraction: The operation of taking away one quantity from another

Difference: The result of a subtraction problem

Minuend: The number being subtracted from

Subtrahend: The number being subtracted

Complete methodology:
  1. Identify parts: Recognize the minuend and subtrahend
  2. Choose strategy: Counting, number bonds, or mental math
  3. Execute calculation: Perform the subtraction
  4. Verify answer: Check through reverse counting or addition
  5. Record result: Write the complete equation
Tip 1: Use the "counting back" strategy when the subtrahend is small.
Tip 2: Start with the larger number and count down.

Tip 3: Use ten frames to visualize numbers.

Tip 4: Look for patterns like doubles (10-5, 8-4).

Common errors: Miscounting, forgetting to count all subtracted, starting from wrong number.

Key concepts: Understanding that subtraction takes away, recognizing number patterns.

Rules to remember:

• Non-commutative: Order matters (15 - 3 ≠ 3 - 15)

• Identity: Subtracting 0 keeps the number the same

• Counting down: Subtraction means moving to smaller numbers

• Verification: Always check your answer

Subtraction Facts Table (11-20)
11-1=10
11-2=9
11-3=8
11-4=7
11-5=6
12-1=11
12-2=10
12-3=9
12-4=8
12-5=7
13-1=12
13-2=11
13-3=10
13-4=9
13-5=8
14-1=13
14-2=12
14-3=11
14-4=10
14-5=9
15-1=14
15-2=13
15-3=12
15-4=11
15-5=10
16-1=15
16-2=14
16-3=13
16-4=12
16-5=11
17-1=16
17-2=15
17-3=14
17-4=13
17-5=12
18-1=17
18-2=16
18-3=15
18-4=14
18-5=13
19-1=18
19-2=17
19-3=16
19-4=15
19-5=14
20-1=19
20-2=18
20-3=17
20-4=16
20-5=15
Solution: Exercises 4 to 5
4 Word Problems
Exercise 4
Emma has 16 stickers. She gives 7 stickers to her friend. How many stickers does Emma have now?
Definition:

Word Problem: A math question written in story form

Real-world Application: Connecting math to everyday situations

Step 1: Identify what we know

Emma starts with 16 stickers

She gives 7 stickers to her friend

Step 2: Identify what we need to find

Total stickers Emma has now

Step 3: Set up the subtraction

Start with - Given = Remaining

16 - 7 = ?

Step 4: Solve using counting

Count: 16, 15, 14, 13, 12, 11, 10, 9

So 16 - 7 = 9

16 - 7 = 9
Final answer:

Emma has 9 stickers now

Applied rules:

• Story understanding: Find the important numbers

• Keyword identification: "Gives" means subtraction

• Problem solving: Convert story to math equation

5 Mixed Subtraction Problems
Exercise 5
Solve: 14 - 6 = ? and 17 - 9 = ?
Definition:

Mixed Problems: Different subtraction problems to practice the method

Consistent Application: Using the same strategy for various problems

Step 1: Solve 14 - 6

Start at 14, count 6 backward: 13, 12, 11, 10, 9, 8

So 14 - 6 = 8

Step 2: Solve 17 - 9

Start at 17, count 9 backward: 16, 15, 14, 13, 12, 11, 10, 9, 8

So 17 - 9 = 8

Step 3: Notice the pattern

Both problems equal 8, but through different paths

Step 4: Verify both answers

Count jumps: 14 - 6 has 6 jumps, 17 - 9 has 9 jumps ✓

14 - 6 = 8
17 - 9 = 8
Final answer:

14 - 6 = 8 and 17 - 9 = 8

Applied rules:

• Consistent method: Same steps work for all problems

• Sequential counting: Always count one number at a time

• Verification: Always check your counting

Subtraction Within 20 - Complete Guide
\(12 - 5 = 7\)
Basic Subtraction Facts
Key definitions:

Subtraction: The mathematical operation of taking away one quantity from another

Within 20: Subtraction problems where the minuend does not exceed 20

Minuend: The number being subtracted from in a subtraction problem

Complete methodology:
  1. Number Recognition: Identify the numbers to be subtracted
  2. Strategy Selection: Choose counting, number bonds, or mental math
  3. Sequential Execution: Perform the subtraction step by step
  4. Result Verification: Check the answer through alternative method
  5. Equation Recording: Write the complete mathematical sentence
Tip 1: Use the "counting back" strategy for smaller subtrahends.

Tip 2: Practice number bonds to build instant recall.

Tip 3: Use ten frames or objects when visualizing is helpful.

Tip 4: Look for patterns like near doubles (12-6, 14-7).

Visual benefits: Concrete objects and visual aids make abstract concepts understandable.

Memory aids: Repeated practice builds automaticity for future math.

Essential formulas:

• Subtraction equation: Minuend - Subtrahend = Difference

• Non-commutative property: a - b ≠ b - a

• Identity property: n - 0 = n

• Counting sequence: Each number is one more than the previous

Subtraction Within 20 Workflow

📊
Step-by-Step Process
1
See Numbers
2
Choose Method
3
Count Down
4
Verify
5
Write
Subtraction Patterns

20 - 1 = 19

19 - 1 = 18

18 - 1 = 17

17 - 1 = 16

16 - 1 = 15

Practice Makes Perfect!

Questions & Answers

Question: Why do we learn subtraction within 20? Isn't that too hard compared to 10?

Answer: Great question! Subtraction within 20 builds on what you learned with 10. Here's why it's important:

  • Building on basics: You already know subtraction within 10, now you're extending it
  • Real-world numbers: We often subtract numbers larger than 10 in daily life
  • Strategy development: You learn helpful tricks like counting back efficiently
  • Preparation: Sets you up for even larger numbers later

Think of it like climbing stairs - you mastered step 1-10, now you're going up to step 20!

Example: 15 - 7 becomes easier when you practice the counting back strategy.

Question: My child sometimes struggles with 13 - 7 and gets confused. What's the best strategy to teach?

Answer: The "counting back" strategy works great for 13 - 7! Here's how:

  • Start with 13: Show 13 objects or draw 13 dots
  • Count back 7: Count backward: 12, 11, 10, 9, 8, 7, 6
  • Land on the answer: The 7th number back is 6
  • Alternative: Think "from 7 to 13 is 6 more"

So: 13 - 7 = 6

Practice this strategy with similar problems like 14 - 6, 15 - 8, 12 - 5 to build the pattern.

Visual aids like number lines help make this concrete!

Question: Sometimes I forget 17 - 5. Do I always have to count from 17?

Answer: At first, counting is perfectly fine! But here are faster ways:

  • Think about tens: 17 is 10 + 7, so 17 - 5 = 10 + 2 = 12
  • Just count back from 17: Just 16, 15, 14, 13, 12 (only 5 numbers)
  • Practice patterns: 17 - 5 = 12, 16 - 4 = 12, 15 - 3 = 12
  • Count on from 5: "5, 6, 7, 8, 9, 10, 11, 12" (that's 7 more)

Start by counting, but over time you'll remember that 17 - 5 = 12 automatically. It takes practice!

Think of it like learning to ride a bike - you start slowly and get faster with practice.

Question: What are some effective ways to practice subtraction within 20?

Answer: Effective practice combines repetition with engagement! Here are strategies:

  • Flashcards: Focus on "hard" facts first
  • Ten frames: Visualize numbers and make subtraction concrete
  • Number line practice: Jump backward to subtract
  • Word problems: Connect math to real situations

Effective practice strategies:

  • Practice 5-10 minutes daily rather than long sessions
  • Focus on patterns like doubles and near doubles
  • Use games like "Subtraction War" with playing cards
  • Practice counting back strategies regularly

The key is consistent, focused practice with immediate feedback!