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addition

Adding multiples of 10

Use place value to add 10, 20 or 30 mentally.

Quick answer

You can add multiples of 10 by counting up in tens, using place value, or by adding the tens together and keeping the ones the same.

Learning outcome

By the end of this page, you will be able to add multiples of 10 mentally, like 20 + 30 or 50 + 40, using place value and number patterns. Success signs:
  • You can add 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 to any number quickly
  • You understand that 30 + 40 means 3 tens + 4 tens = 7 tens
  • You can use place value to help you add numbers like 24 + 30
  • You can solve problems like “I have 40 stickers, and my friend gives me 50 more. How many do I have?”

Why this matters

Adding multiples of 10 helps you solve problems quickly and easily. It's useful when you're counting money, adding up scores in a game, or figuring out how many items you have. It's also a great building block for bigger addition problems and mental maths. In games like Minecraft, you might need to add up how many blocks you have in different piles. In real life, if you're saving up money or counting your pocket money, you’ll often add multiples of 10. This skill helps you think fast and feel confident with numbers.

How it works

Adding multiples of 10 is simple if you understand place value. Each number has a tens digit and a ones digit. When you add multiples of 10, you're just adding the tens together. Let’s look at a few ways to do this: Method 1: Counting in tens If you want to add 30 + 40, you can count up in tens: 30, 40, 50, 60, 70. So, 30 + 40 = 70. Method 2: Adding the tens together You can think of 30 as 3 tens and 40 as 4 tens. So 3 tens + 4 tens = 7 tens = 70. Method 3: Using place value If you have 24 + 30, you can think of it as 24 + 30 = 20 + 4 + 30 = 50 + 4 = 54. This way, you're just adding the tens together and keeping the ones the same.

Examples you can see

Let’s look at some examples to help you understand. Example 1: 20 + 30 You have 20 apples and your friend gives you 30 more. How many apples do you have? - 20 = 2 tens - 30 = 3 tens - 2 tens + 3 tens = 5 tens = 50 apples Example 2: 50 + 20 You have 50 marbles and find 20 more. How many marbles? - 50 = 5 tens - 20 = 2 tens - 5 tens + 2 tens = 7 tens = 70 marbles Example 3: 40 + 60 You collect 40 stamps and then get 60 more. How many stamps? - 40 = 4 tens - 60 = 6 tens - 4 tens + 6 tens = 10 tens = 100 stamps Example 4: 34 + 50 You have 34 stickers and get 50 more. How many? - 34 = 3 tens + 4 ones - 50 = 5 tens - 3 tens + 5 tens = 8 tens = 80 - Add the ones: 80 + 4 = 84 stickers

Try it as a mini adventure

Adventure: The Treasure Hunt You are on a treasure hunt with your friend. You start with 30 gold coins. Then, you find a chest with 40 more coins. Next, you discover another chest with 20 more coins. How many coins do you have now? Let’s solve this step by step: 1st time: You start with 30 coins. 2nd time: You find 40 more coins. 30 + 40 = 70 coins. 3rd time: You find 20 more coins. 70 + 20 = 90 coins. You now have 90 coins! Great job, treasure hunter! You can also draw a simple picture to show your coins:
  • Draw 30 circles for your first coins
  • Draw 40 more circles for the second chest
  • Draw 20 more circles for the third chest
Count them all together to see how many you have!

Common mistakes

  • Mistake: Adding 30 + 40 and getting 700 instead of 70. Why it happens: The child might be thinking about hundreds instead of tens. Fix: Use base-10 blocks or draw tens to help see that 3 tens + 4 tens = 7 tens = 70.
  • Mistake: Adding 24 + 30 and getting 54 instead of 54. Why it happens: The child adds the tens correctly but forgets to add the ones. Fix: Show that 24 + 30 = 20 + 4 + 30 = 50 + 4 = 54.
  • Mistake: Thinking 50 + 60 = 110. Why it happens: Confusion with place value or counting. Fix: Practice with counting in tens and visualising the groups of ten.

Parent and carer guide

As a parent or carer, you can help your child by:
  • Using everyday objects like coins, blocks, or counters to show tens and ones
  • Practising counting in tens together: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100
  • Using real-life situations like shopping or games to practice adding multiples of 10
  • Encouraging your child to explain how they solved a problem
  • Not worrying if they make mistakes – it’s part of learning!
What to say:
  • “Let’s count how many tens we have together.”
  • “Can you show me with your blocks?”
  • “What happens when you add 30 and 40?”
What not to do:
  • Don’t rush or say “hurry up” – take time to understand
  • Don’t say “that’s wrong” – instead, ask “how did you think about it?”
  • Don’t compare your child to others

Practice questions

  1. What is 10 + 20?
  2. What is 30 + 50?
  3. What is 40 + 60?
  4. What is 24 + 30?
  5. What is 50 + 40?
  6. What is 70 + 20?
  7. What is 35 + 40?
  8. What is 60 + 30?
  9. What is 80 + 10?
  10. What is 27 + 50?
Answers:
  1. 30
  2. 80
  3. 100
  4. 54
  5. 90
  6. 90
  7. 75
  8. 90
  9. 90
  10. 77

FAQ

What does "multiples of 10" mean?

Multiples of 10 are numbers that can be made by multiplying 10 by a whole number. Examples include 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100.

Why is it helpful to add multiples of 10?

Adding multiples of 10 helps you solve problems faster and makes mental maths easier. It also helps you understand place value and number patterns.

How can I practice adding multiples of 10?

You can practice by using coins, blocks, or drawing tens. Try solving problems like 30 + 40 or 60 + 20. You can also play games or use apps that focus on place value.

Can I add 10 to any number?

Yes! You can add 10 to any number. For example, 23 + 10 = 33, and 56 + 10 = 66.

How do I know if I got the right answer?

You can check your answer by counting up in tens or by using a number line. You can also add the tens and ones separately and see if it makes sense.