Checking multiplication answers

Quick answer

You can check if your multiplication is correct by using division (the inverse operation), making a rough estimate, or by doing the multiplication again using a different method.

Learning outcome

By the end of this page, you will be able to check if your multiplication answers are correct using at least one of three methods: division, estimation, or reworking the calculation.

• You can use division to check if your multiplication is right.
• You can make a quick guess to see if your answer is in the right ballpark.
• You can try multiplying again using a different method to double-check.

Why this matters

Checking your multiplication helps you catch mistakes and build confidence in your maths. It's like being a detective for numbers! Whether you're sharing snacks, planning a party, or helping with your homework, checking your answers makes sure you're not making silly errors. In real life, you might be counting how many cookies you need for a bake sale or working out how many tiles you need for your bedroom floor. If you get the multiplication wrong, you could end up with too many or too few cookies, or too many or too few tiles!

How it works

There are three main ways to check your multiplication:

1. Use division (the inverse operation): If you multiply a by b to get c, then c divided by a should give you b.
2. Make an estimate: Round your numbers to make a simpler calculation and see if your answer is close.
3. Rewrite the multiplication: Try doing the multiplication again, perhaps using a different method like repeated addition or an array.

Examples you can see

Let’s look at an example: 6 × 7 = 42.

Method 1: Using division

Since 6 × 7 = 42, we can check by dividing 42 by 6. If we get 7, then our multiplication was correct!

42 ÷ 6 = 7

Great! So 6 × 7 = 42 is correct.

Method 2: Making an estimate

If we're not sure about 6 × 7, we can round it to 5 × 10 = 50. Since 42 is close to 50, it looks like a good answer.

Method 3: Rewriting the multiplication

We can also check by adding 7 six times: 7 + 7 + 7 + 7 + 7 + 7 = 42. This is the same as 6 × 7, so we're confident in our answer.

Try it as a mini adventure

Adventure: The Cookie Shop Mystery

You are a detective in a cookie shop. The shopkeeper says they sold 8 boxes of cookies, with 9 cookies in each box. They claim they sold 72 cookies in total. But you suspect there might be a mistake. Can you check if the shopkeeper is right?

Step 1: Multiply to see what 8 × 9 should be.

8 × 9 = 72

Step 2: Use division to check. If 72 ÷ 8 = 9, then the shopkeeper is correct.

72 ÷ 8 = 9

Step 3: Make an estimate. Round 8 to 10 and 9 to 10. 10 × 10 = 100. Since 72 is less than 100, it's reasonable.

Step 4: Try adding 9 eight times. 9 + 9 + 9 + 9 + 9 + 9 + 9 + 9 = 72

Great detective work! You found that 8 × 9 = 72 is correct. The shopkeeper was telling the truth!

Common mistakes

• Mistake: Thinking that 7 × 8 = 54.
• Why it happens: A child might confuse the times table and forget that 7 × 8 = 56.
• How to fix it: Use division to check: 54 ÷ 7 = 7.7, which is not a whole number, so 54 is not correct. The right answer is 7 × 8 = 56.

• Mistake: Forgetting to carry numbers when multiplying.
• Why it happens: It's easy to miss a number when doing long multiplication.
• How to fix it: Double-check each step and use the division method to verify your final answer.

• Mistake: Adding instead of multiplying.
• Why it happens: A child might accidentally add numbers instead of multiplying them.
• How to fix it: Use the repeated addition method to check if it matches the multiplication result.

Parent and carer guide

Helping your child check multiplication answers is a great way to build their confidence and understanding. Here are a few tips:

• Encourage them to try at least one method to double-check their work.
• Ask them to explain how they checked their answer – this helps them think more deeply about maths.
• Use real-life examples like shopping or cooking to make it more relevant.
• Don’t worry if they make mistakes – that’s how we learn!
• Use games or puzzles to make checking fun, like creating a multiplication maze where they must check their answers to find the exit.

Remember: The goal is not to make your child perfect, but to help them become confident and curious mathematicians.

Practice questions

1. Check if 5 × 6 = 30 is correct using division.
2. Estimate 7 × 8 and see if 56 is close.
3. Use repeated addition to check 4 × 9 = 36.
4. Check if 9 × 7 = 63 using division.
5. Estimate 6 × 11 and compare with 66.

Answers:

1. 30 ÷ 5 = 6, so 5 × 6 = 30 is correct.
2. 7 × 8 ≈ 10 × 10 = 100. 56 is close, so it's reasonable.
3. 9 + 9 + 9 + 9 = 36, so 4 × 9 = 36 is correct.
4. 63 ÷ 9 = 7, so 9 × 7 = 63 is correct.
5. 6 × 11 ≈ 10 × 10 = 100. 66 is close, so it's reasonable.

FAQ

Why should I check my multiplication?

Checking your multiplication helps you catch mistakes and makes sure you’re confident in your answers. It’s like being a detective for numbers!

What is the inverse operation of multiplication?

The inverse operation of multiplication is division. If you multiply two numbers, you can divide the answer by one of them to get the other number.

Can I use estimation to check multiplication?

Yes! Estimation helps you see if your answer is in the right ballpark. It's a quick way to spot if a mistake was made.

What if I get different answers when I check?

If you get different answers, it means you might have made a mistake. Go back and try again using one of the checking methods. You can also ask a friend or grown-up to help you check.

How can I make checking multiplication fun?

You can turn it into a game, like a detective mystery, or use real-life situations like cooking or sharing snacks. Making it part of a story or challenge helps!