Question

A few cookies are eaten from a packet that had $18$ cookies in total. If the number of cookies left is the same as the number of cookies eaten, select the equation to find the number of cookies left in the packet.

• A. $18-9=9$
• B. $9-18=9$
• C. $8-18=8$
• D. $18-8=8$

Answer 1

The correct option is A $18-9=9$

Solution: Option B

Say: The total number of cookies is given, out of which a few are eaten.

Ask:
What is the total number of cookies?
Ans: $18$

What does the question say about the number of cookies eaten and what are left in the packet?
Ans: The number of cookies eaten and number of cookies left in the packet is the same.

Which option gives us the number of cookies left in the packet?
Ans: Option B

Why do you think so?
Ans: Option A and D show incorrect subtraction equations, as we cannot subtract a smaller number from a greater number. Here, $9$ in Option A and $8$ in Option D are smaller than $18$. Option C is incorrect because $18–8=10$ and not $8$. In Option B we are subtracting the smaller number, i.e., $9$ from the greater number, i.e., $18$ to get a difference of $9$.

So, what is the number of cookies left in the packet?
Ans: $9$. Here, we can see that the number $9$ is used two times in the equation, as both the number of cookies eaten and that are left in the packet is 9 each.

Hence, Option B is correct.


WB: If required, use the whiteboard to represent the total number of cookies using counters on a number frame. Then cross out the number of cookies that were eaten as shown and write the subtraction equation.