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Subtraction as take away

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visibility 73update 2 months agobookmarkshare

🎯 In this topic you will

Subtract by taking away a part from a whole.

🧠 Key Words

subtract
take away

Show Definitions

subtract: To find the difference between numbers by removing one amount from another.
take away: A method of subtraction where objects or numbers are removed from a total to find what remains.

🍎 Taking Some Away

If there are too many, you might need to take some away. You can write your subtraction in words or in a number sentence.

❓ EXERCISES

1. Cross out $1$ bead and $1$ counter. Count how many there are now.

👀 Show answer

There are $7$ beads. Taking away $1$ leaves $6$. There are $5$ counters. Taking away $1$ leaves $4$. So $7 - 1 = 6$ and $5 - 1 = 4$.

🧠 Think like a Mathematician

Task: Investigate how a domino pattern changes when one counter is taken away each time.

Method:

Put $9$ counters on the table in the domino pattern.
Take one counter away to make the domino pattern for $8$.
Take one counter away again to make the domino pattern for $7$.
Repeat until there are no counters left.

Follow-up Questions:

1. What number pattern do you notice as you remove one counter each time?

2. How many steps does it take to reach zero counters?

3. Write the subtraction pattern you observed.

Show Answers

1: The numbers decrease by $1$ each time (for example: $9, 8, 7, 6, \dots, 0$).
2: It takes $9$ steps to go from $9$ counters to $0$.
3: The subtraction pattern is $9 - 1 = 8,\; 8 - 1 = 7,\; 7 - 1 = 6,\; \dots,\; 1 - 1 = 0$.

📘 Worked example

Write a sentence for the story.

Answer:

There were $5$ ducks in the pond. $2$ ducks left the pond. There are $3$ ducks left in the pond. $5$ take away $2$ equals $3$. The number sentence is $5 - 2 = 3$.

Start by counting the ducks in the pond. There are 5 ducks.

Next, notice that 2 ducks leave the pond.

Subtract to find how many remain: $5 - 2 = 3$. So, 3 ducks are left in the pond.

❓ EXERCISES

2. Tell your partner what is happening in this story. Write the sentences.

👀 Show answer

There were $6$ children. $2$ children ran away. There are $4$ children left. The number sentence is $6 - 2 = 4$.

3. Write the number sentence for this story.

👀 Show answer

$5 - 1 = 4$.

4. Write the number sentence for this story.

👀 Show answer

There were $5$ birds. $3$ birds flew away. There are $2$ birds left. The number sentence is $5 - 3 = 2$.

📘 Worked example

$4$ take away $3$ equals $\square$

$4 - 3 = \square$

Answer:

$4$ take away $3$ equals $1$.

$4 - 3 = 1$

$4$ is the whole, so place $4$ counters in the whole circle.

$3$ is the part to take away, so move $3$ counters into the first part circle.

Move what is left into the other part circle. The remaining counters show that $4 - 3 = 1$.

❓ EXERCISES

5. Find out how many are left over after taking a part away from the whole. Use the diagram to help you. Estimate your answer first.

👀 Show answer

$10 - 3 = 7$
$9 - 4 = 5$
$8 - 5 = 3$
$7 - 6 = 1$

6. Complete each part-whole diagram. Estimate your answer first. Write a number sentence for each diagram.

👀 Show answer

$7 - 3 = 4$
$10 - 4 = 6$

7. Complete each subtraction wall.

👀 Show answer

First wall: missing number is $3$ because $9 - 6 = 3$.
Second wall: missing number is $5$ because $8 - 3 = 5$.
Third wall: missing numbers are $8$ and $6$ because $10 - 2 = 8$ and $8 - 2 = 6$.
Fourth wall: missing numbers are $4$ and $1$ because $7 - 3 = 4$ and $4 - 2 = 2$.

🧠 Think like a Mathematician

Task: Choose any two of these numbers: $4,\;6,\;8,\;10$. Choose again and subtract the smaller number from the larger number. Do this at least $4$ times. What do you notice?

Method:

Pick any two numbers from $4,\;6,\;8,\;10$.
Subtract the smaller number from the larger number.
Record your result.
Repeat the process at least $4$ times using different pairs.
Look for a pattern in your answers.

Follow-up Questions:

1. What do you notice about the answers you get?

2. Are the results odd or even numbers?

3. Explain why this happens.

Show Answers

1: The answers are always even numbers (such as $2,\;4,\;6$).
2: The results are even.
3: This happens because you are subtracting one even number from another even number, and even minus even is always even.

📘 What we've learned

We learned that subtraction means taking away a part from a whole.
We can write subtraction using number sentences such as $a - b = c$.
We used part–whole diagrams to help find what is left.
We practiced estimating answers before calculating exactly.
We noticed that subtracting even numbers from even numbers gives an even result.

Subtraction as take away

🎯 In this topic you will

🧠 Key Words

🍎 Taking Some Away

❓ EXERCISES

🧠 Think like a Mathematician

❓ EXERCISES

❓ EXERCISES

🧠 Think like a Mathematician

📘 What we've learned

Related Past Papers

Related Tutorials

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