Subtraction Within 20

In this article, we will be learning subtraction within 20. Let’s start with a recap!

Subtraction within 10

Example: 

James had some paper clips. He lost some of them. How many paper clips did James have left? 

He had __________ paper clips left. 

Answer: 

4

Explanation:

Count the total number of paper clips and subtract the number of paper clips that are crossed out. We get:

Question 1: 

Rachel had 8 bottles of water. She gave away 5 bottles of water. How many bottles of water does Rachel have left?

1. 1
2. 2
3. 3
4. 13

Answer:

(3) 3

Explanation:

Question 2: 

There are 10 ducks. 2 ducks are in the pond. How many of them are not in the pond?

Answer:

(4) 8

Explanation: 

Question 3: 

Mr Tan has 10 pens. He gives away 3 pens. How many pens does he have left?

1. 6
2. 7
3. 8
4. 13

Answer:

(2) 7

Explanation: 

Subtraction with 20 by subtracting the ones first

Example:

Nina had 17 pencils. She lost 6 pencils. How many pencils did she have left?

Nina has __________ pencils left.

Answer:

11

Explanation:

Split 17 into 10 and 7. Subtract 6 from 7. Add the answer to 10. 

Step 1: 

\(17 = 10 + 7\)

Step 2: 

Subtract the ones. 

Step 3:

\(\begin{align}​ 7 – 6 &= 1 \\ 10 + 1 &= 11 \end{align}\)

Question 1: 

Complete the equation.

1. 13
2. 14
3. 15
4. 16

Answer:

(3) 15

Explanation: 

Split 18 into 10 and 8. Subtract 3 from 8. Add the answer to 10.

Step 1:

\(18 = 10 + 8\)

Step 2: 

Subtract the ones.

Step 3: 

\(\begin{align}​ 8 – 3 &= 5 \\ 10 + 5 &= 15 \end{align} \)

Question 2:

Complete the equation.

1. 13
2. 15
3. 16
4. 17

Answer:

(4) 17

Explanation:

Split 19 into 10 and 9. Subtract 2 from 9. Add the answer to 10.

Step 1:

\(19 = 10 + 9\)

Step 2:

Subtract the ones.

Step 3: 

\(\begin{align}​ 9 – 2 &= 7 \\ 10 + 7 &= 17 \end{align}\)

Subtraction with 20 by subtracting from 10 first

Example:

Amy had 16 buttons. She gave 8 buttons to her sister. How many buttons did Amy have left?

Answer:

8

Explanation:

Split 16 into 10 and 6. Subtract 8 from 10. Add the answer to 6. 

Step 1: 

\(16 = 6 + 10\)

Step 2:

Subtract from 10 first.

Step 3:

\(\begin{align}​ 10 - 8 &= 2 \\ 6 + 2 &= 8 \end{align} \)

Question 1: 

Fill in the blank with the correct answer.

\(13 - 5 =\) __________

1. 8
2. 9
3. 12
4. 18

Answer:

(1) 8

Explanation: 

Step 1:

\(13 = 10 + 3\)

Step 2:

Subtract from 10. 

Step 3:

\(\begin{align}​ 10 - 5 &= 5 \\ 5 + 3 &= 8 \end{align}\)

Question 2: 

Fill in the blank with the correct answer:

\(20 - 2 =\) __________

1. 8
2. 10
3. 12
4. 18

Answer:

(4) 18

Explanation: 

Step 1:

\(20 = 10 + 10\)

Step 2:

Subtract from 10. 

Step 3:

\(\begin{align}​ 10 - 2 &= 8 \\ 8 + 10 &= 18 \end{align}\)

Question 3: 

Fill in the blank:

\(17 - 9 =\) __________

1. 7
2. 8
3. 9 
4. 10

Answer:

(2) 8

Explanation:

Step 1:

\(17 = 10 + 7\)

Step 2:

Subtract from 10. 

Step 3:

\(\begin{align}​ 10 - 9 &= 1 \\ 1 + 7 &= 8 \end{align}\)

Question 4:

Which of the following subtraction equations best represents the diagram below? 

1. \(19 - 6 = 12\)
2. \(19 - 6 = 13\)
3. \(20 - 6 = 13\)
4. \(20 - 6 = 14\)

Answer:

(2) \(19 - 6 = 13\)

Explanation: 

Identify the total number of cupcakes and subtract the 6 cupcakes that are crossed out. 

Step 1:

\(19 = 10 + 9\)

Step 2:

Subtract from 10. 

Step 3:

\(\begin{align}​ 10 - 6 &= 4 \\ 4 + 9 &= 13 \end{align}\)

Question 5:

Which of the following equations best represents the diagram below?

1. \(13 + 2 = 5\)
2. \(13 - 2 = 11\)
3. \(13 - 3 = 10\)
4. \(13 - 10 = 3\)

Answer:

(2) \(13 - 2 = 11\)

Explanation: 

Identify the total number of pumpkins and subtract the 2 pumpkins that are crossed out.

Step 1:

\(13 = 10 + 3\)

Step 2:

Subtract from 10. 

Step 3:

\(\begin{align}​ 10 - 2 &= 8 \\ 8 + 3 &= 11 \end{align}\)

Question 6:

Which of the following equations best represents the diagram below?

1. \(10 - 4 = 6\)
2.   \(4 + 6 = 10\)
3. \(12 - 4 = 8\)
4.   \(6 + 6 = 12\)

Answer:

(3) \(12 - 4 = 8\)

Explanation: 

Identify the total number of birds and subtract the 4 birds that are crossed out.

Step 1:

\(12 = 10 + 2\)

Step 2:

Subtract from 10 first.

Step 3:

\(\begin{align}​ 10 - 4 &= 6 \\ 6 + 2 &= 8 \end{align}\)

Question 7:

There were 17 apples. Tom ate 3 of them. How many apples are left now?

1. \(14 - 3 = 11\)
2. \(14 - 4 = 10\)
3. \(17 - 4 = 13\)
4. \(17 - 3 = 14\)

Answer:

(4) \(17 - 3 = 14\)

Explanation: 

Identify the total number of apples and subtract the 3 apples that were eaten.

Step 1:

\(17 = 10 + 7\)

Step 2:

Subtract from 10 first.

Step 3:

\(\begin{align}​ 10 - 3 &= 7 \\ 7 + 7 &= 14 \end{align} \)

Question 8:

Which of the following is equal to 7?

Answer:

(4) \(15 - 8 = 7\)

Explanation: 

1. \(20 - 3 = 17\)
2. \(19 - 7 = 12\)
3. \(18 - 3 = 15\)
4. \(15 - 8 = 7\)

Question 9: 

Which of the following is not equal to 11?

Answer:

(2) \(16 - 6 = 10\)

Explanation: 

1. \(10 + 1 = 11\)
2. \(16 - 6 = 10\)
3. \(13 - 2 = 11\)
4.   \(9 + 2 = 11\)

Question 10:

Which of the following number sentences is correct?

Answer:

(2) \(13 - 8 = 5\)

Explanation: 

1. \(10 - 7 = 3 \quad \text{ (wrong)}\)
2. \(13 - 8 = 5 \quad\text{ (correct)}\)
3. \(19 - 6 = 13 \quad\text{(wrong)}\)
4. \(12 - 8 = 4 \quad\text{ (correct)}\)

Question 11:

Which of the following number sentences has the greatest answer?

Answer: 

(2) \(16 - 3 = 13\)

Explanation:

1. \(14 - 7 = 7\)
2. \(16 - 3 = 13\)
3. \(17 - 8 = 9\)
4. \(20 - 9 = 11\)

Out of all the answers, 13 is the greatest.

In this article, we have learnt  

• Subtraction Within 20