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Maths Adventures

Treehouse maths quest: decimals

A story-led junior maths adventure using ladders, plans and height measurements to measure small distances, money and scores with tenths and hundredths.

Quick answer

Decimals are numbers that show parts of a whole, like 0.5 or 0.25. In a Treehouse maths quest, you might use decimals to measure how tall your ladder is, or to work out how much money you have if you have 3.75 pounds.

Learning outcome

By the end of this page, you will understand how decimals work and how to use them to measure small parts of things, like heights, money, or scores. Success signs:
  • You can see that 0.5 is half of one whole
  • You can compare two decimal numbers like 0.3 and 0.6
  • You can add decimals together, like 0.4 + 0.2
  • You can use decimals in real-life situations like measuring your treehouse ladder or counting your pocket money

Why this matters

Decimals help us measure and count things more precisely. When you build a treehouse, you need to know if your ladder is 2.5 metres tall, not just 2 metres. When you play a game and score 12.7 points, you are using decimals. In the real world, decimals are used for money, time, cooking, science, and even video games.

How it works

Decimals are numbers that come after the decimal point. The first digit after the decimal point shows tenths (like half a pizza). The second digit shows hundredths (like a quarter of a pizza). When we write 0.4, it means 4 tenths. When we write 0.25, it means 25 hundredths. Think of a pizza cut into 10 equal slices. If you eat 4 slices, you have eaten 0.4 of the pizza. If you eat 25 slices out of 100, you have eaten 0.25 of the pizza.

Examples you can see

Let’s imagine you are building a treehouse and you need to measure the height of your ladder. Example 1: Measuring a Ladder Your ladder is 2.7 metres tall. This means:
  • 2 whole metres
  • 0.7 of another metre
Example 2: Counting Money You have 3.45 pounds. This means:
  • 3 whole pounds
  • 0.4 of a pound (40 pence)
  • 0.05 of a pound (5 pence)
Example 3: Scoring in a Game In your treehouse game, you score 15.8 points. This means:
  • 15 whole points
  • 0.8 of another point (8 tenths of a point)

Try it as a mini adventure

Treehouse Maths Quest: The Ladder Challenge You are building a treehouse and need to measure your ladder. You have a ladder that is 3.2 metres tall. You also have a small step that is 0.5 metres tall. You want to know how tall your ladder and step are together. Step 1: Write down the height of your ladder: 3.2 metres Step 2: Write down the height of your step: 0.5 metres Step 3: Add them together:
  • 3.2 + 0.5 = ?
Step 4: Count how many tenths you have:
  • 2 tenths + 5 tenths = 7 tenths
  • 3 whole metres + 0 whole metres = 3 whole metres
  • Answer: 3.7 metres
Step 5: Draw your ladder and step to show the total height.

Common mistakes

  • Mistake: Thinking 0.4 is the same as 0.40
    Why it happens: Children sometimes think the extra zero doesn’t matter.
    Fix: Explain that 0.4 and 0.40 are the same. 0.4 means 4 tenths, and 0.40 means 40 hundredths, which is also 4 tenths.
  • Mistake: Adding 0.3 + 0.2 and getting 0.5
    Why it happens: Children might forget that 0.3 + 0.2 = 0.5, but think it should be 5.
    Fix: Show that 3 tenths + 2 tenths = 5 tenths, which is 0.5.
  • Mistake: Comparing 0.6 and 0.45 and saying 0.45 is bigger
    Why it happens: Children might focus on the number of digits instead of the value.
    Fix: Show that 0.6 = 0.60, so 0.60 is bigger than 0.45.

Parent and carer guide

How to help your child learn about decimals:
  • Use real-life examples like measuring ingredients when cooking
  • Count money together, especially when dealing with pence
  • Play games that involve decimals, like board games with dice that show decimal numbers
  • Use a number line to show how decimals fit between whole numbers
  • Ask your child to explain what 0.5 means in different situations
What to say:
  • "Can you show me how 0.5 is the same as half?"
  • "If we have 3.25 pounds, how much is that in pence?"
  • "What does 0.75 mean in terms of a pizza?"
What not to worry about:
  • Your child might make mistakes at first. That's normal!
  • Don't rush them. Take time to explain and practice.
  • Keep it fun and practical, not like a test.

Practice questions

  1. What is 0.3 + 0.4?
  2. Which is bigger: 0.6 or 0.58?
  3. How much is 2.75 + 1.25?
  4. What is 0.9 - 0.4?
  5. How many tenths are in 0.6?
Answers:
  1. 0.7
  2. 0.6
  3. 4.00
  4. 0.5
  5. 6

FAQ

What are decimals?

Decimals are numbers that show parts of a whole. They use a decimal point to separate whole numbers from parts.

How do I read decimals?

You read 0.5 as "five tenths" and 0.25 as "twenty-five hundredths".

Why do we use decimals?

We use decimals to be more precise when measuring or counting. For example, a ladder might be 2.7 metres tall, not just 2 metres.

How are decimals used in money?

In money, 0.25 pounds is 25 pence, and 0.50 pounds is 50 pence.

How can I practice decimals at home?

You can practice by measuring things around your house, counting money, or playing games that involve decimal numbers.