Multiplying by multiples of 10

Quick answer

When you multiply by multiples of 10 (like 20, 30, 40), you can use place value to make it easier. Multiply the non-zero digits first, then add the zeros.

Learning outcome

By the end of this page, you will be able to multiply any number by 20, 30, 40, and other multiples of 10 using place value and simple steps.

• You can multiply 3 by 20 and get 60
• You can explain why 4 × 50 = 200
• You can use the pattern of adding zeros to solve multiplication problems
• You can check your answers using a different method

Why this matters

Multiplying by multiples of 10 is a super helpful skill in everyday life. You might need it when you're shopping and want to know how much 3 packets of 20 stickers cost, or when you're planning a party and need to work out how many cups you'll need if there are 40 guests and each person gets 2 cups.

It's also useful in games, like when you're building with LEGO and need to know how many bricks you'll use for 30 towers, or when you're playing football and counting how many goals each team scores if each goal is worth 10 points.

Understanding this pattern helps you solve bigger multiplication problems quickly and confidently. It's a key step in building strong maths skills for later!

How it works

When you multiply by multiples of 10, here’s how to think about it:

1. First, multiply the non-zero digits (the numbers that are not 0)
2. Then, count how many zeros are in the multiple of 10
3. Add that many zeros to your answer

Let’s break it down:

For example, 5 × 30:

1. First, multiply 5 × 3 = 15
2. Then, count the zeros in 30. There is 1 zero.
3. So, add 1 zero to 15, which gives you 150.

It’s like saying 5 groups of 30, which is the same as 5 groups of 3 tens. So 5 × 3 = 15, and 15 tens = 150.

Examples you can see

Here are some examples to help you understand how this works:

Try to think of it like this: 2 × 80 is the same as 2 × 8 × 10. So you multiply 2 × 8 = 16, then multiply by 10 to get 160.

Let’s try a slightly harder one:

9 × 30:

1. 9 × 3 = 27
2. 30 has 1 zero
3. So, 27 + 1 zero = 270

And here’s a challenge:

4 × 70:

1. 4 × 7 = 28
2. 70 has 1 zero
3. So, 28 + 1 zero = 280

Try it as a mini adventure

Imagine you are a space explorer on a mission to collect alien coins. Each alien coin is worth 10 units. You need to collect coins for 5 different planets. Each planet gives you 30 coins. How many coins do you collect in total?

Let’s solve this step by step:

1. How many coins per planet? 30 coins
2. How many planets? 5 planets
3. So, 5 × 30 = ?

Using our method:

1. 5 × 3 = 15
2. 30 has 1 zero
3. So, 15 + 1 zero = 150

You collect 150 coins in total!

Now, imagine you also collect 40 coins from a space station. How many coins do you have now?

1. 150 + 40 = ?

Let’s think: 150 + 40 = 190

You now have 190 coins!

Common mistakes

• Mistake: Adding too many zeros. For example, 3 × 40 = 1200 instead of 120.
• Why it happens: Forgetting that 40 only has 1 zero, not 2.
• Fix: Count the zeros in the multiple of 10 carefully.

• Mistake: Multiplying the wrong numbers. For example, 6 × 50 = 300, but thinking 6 × 5 = 30 and adding 2 zeros.
• Why it happens: Not separating the non-zero digits from the zeros.
• Fix: Always multiply the non-zero digits first, then add the zeros.

• Mistake: Forgetting to add zeros at all. For example, 7 × 20 = 14 instead of 140.
• Why it happens: Thinking it's just regular multiplication.
• Fix: Always check how many zeros are in the multiple of 10 and add that many to your answer.

Parent and carer guide

Helping your child with multiplying by multiples of 10 can be fun and easy!

• Use everyday examples: When you're shopping, ask how much 4 packets of 30 stickers cost, or how many wheels 5 toy cars have if each has 10 wheels.
• Practice with place value: Show them that 30 is 3 tens, so 3 × 30 = 3 × 3 × 10 = 9 × 10 = 90.
• Ask questions: Ask them to explain their thinking. “How did you get 6 × 40 = 240?”
• Encourage checking: After solving, have them double-check by using repeated addition or a different method.
• Be patient: It takes time to build up this skill. Celebrate small wins!

Remember, this is a skill that builds on place value understanding. If your child is struggling, go back to basics with counting in tens, then move to multiplying by 10, and then to multiples of 10.

Practice questions

1. 2 × 30 = ?
2. 5 × 60 = ?
3. 8 × 40 = ?
4. 3 × 90 = ?
5. 7 × 20 = ?
6. 9 × 50 = ?
7. 4 × 80 = ?
8. 6 × 70 = ?
9. 1 × 100 = ?
10. 10 × 10 = ?

Answers:

1. 60
2. 300
3. 320
4. 270
5. 140
6. 450
7. 320
8. 420
9. 100
10. 100

FAQ

How do I know how many zeros to add?

Count the zeros in the multiple of 10. For example, 40 has 1 zero, 70 has 1 zero, 100 has 2 zeros.

Can I use this method for any number?

Yes! You can multiply any number by 20, 30, 40, 50, 60, 70, 80, 90, 100, and so on.

What if I forget to add the zeros?

Double-check your answer by using repeated addition or by thinking of the problem in terms of place value.

Is this the same as multiplying by 10?

Yes, but with multiples of 10, you multiply the non-zero digits first, then add the zeros. For example, 3 × 10 = 30, and 3 × 20 = 60.

Why is this useful?

It helps you solve bigger multiplication problems quickly, especially when dealing with real-life situations like shopping, measuring, or planning.