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Maths Adventures

Sailing maths quest: decimals

A story-led junior maths adventure using maps, bearings and voyage planning to measure small distances, money and scores with tenths and hundredths.

Quick answer

You can use decimals when measuring small distances, counting money, and scoring in sailing to show parts of a whole, like one-tenth or one-hundredth of a kilometre, pound, or point.

Learning outcome

By the end of this page, you will be able to use decimals to measure small distances, count money, and score points in sailing, showing parts of a whole like tenths and hundredths. Success signs:
  • You can read and write decimals like 0.5, 0.25, 1.75
  • You can use decimals to measure distances in metres or kilometres
  • You can add and subtract decimals when counting money or points
  • You can use decimals to show parts of a whole in real-life sailing situations

Why this matters

Decimals are used in sailing to measure small distances, count money, and score points. When you sail, you might measure a distance as 0.5 km, or spend £2.75 on snacks. You might score 1.2 points for a good sail. Understanding decimals helps you make sense of these small parts and use them in real-life sailing adventures.

How it works

Decimals are a way to show parts of a whole number. They use a decimal point (.) to separate the whole number from the parts. For example:
  • 0.5 means 5 parts out of 10
  • 0.25 means 25 parts out of 100
  • 1.75 means 1 whole and 75 parts out of 100
Decimals are like sharing. If you have one pizza and split it into 10 equal slices, one slice is 0.1 of the pizza. If you split it into 100 slices, one slice is 0.01 of the pizza.

Examples you can see

Let's imagine you are planning a sailing trip with your friends. Example 1: Measuring distance You sail 1.5 km on the first day and 2.75 km on the second day. To find the total distance, you add:
  • 1.5 km + 2.75 km = 4.25 km
Example 2: Counting money You buy snacks for £3.20 and drinks for £1.95. To find the total cost:
  • £3.20 + £1.95 = £5.15
Example 3: Scoring points You get 0.5 points for a good sail, and your friend gets 1.25 points. To find the total points:
  • 0.5 + 1.25 = 1.75 points

Try it as a mini adventure

Adventure: The Sailing Maths Quest You are on a sailing adventure with your crew. You need to solve maths puzzles to find treasure on a secret island. Step 1: You sail 1.5 km from the harbour. Then you sail 2.25 km more. How far have you sailed in total?
  • 1.5 km + 2.25 km = ? km
Step 2: You find a treasure chest with £4.30 inside. You spend £1.75 on a new map. How much money do you have left?
  • £4.30 - £1.75 = ?
Step 3: You score 0.75 points for your first sail, and 1.25 points for your second. What is your total score?
  • 0.75 + 1.25 = ? points
Step 4: You measure a distance to the island as 3.6 km. You need to travel 0.4 km more to reach it. How far is the island from your starting point?
  • 3.6 km + 0.4 km = ? km
Step 5: You have £6.50 and want to buy snacks that cost £2.25 each. How many snacks can you buy?
  • £6.50 ÷ £2.25 = ? snacks

Common mistakes

  • Mistake: Adding decimals without lining up the decimal points.
    Why it happens: Children may forget that the decimal point must be in the same column.
    Fix: Always write the decimal points in the same column and add like this:
    1.5
    + 2.25
    3.75
  • Mistake: Thinking 0.5 is bigger than 0.75.
    Why it happens: Children may focus only on the first digit after the decimal point.
    Fix: Compare the digits from left to right: 0.75 = 75 parts of 100, while 0.5 = 50 parts of 100.
  • Mistake: Forgetting to add a zero when subtracting decimals.
    Why it happens: Children may not understand that 1.2 = 1.20.
    Fix: Add a zero to make the decimals the same length:
    2.50
    - 1.20
    1.30

Parent and carer guide

How to help your child:
  • Encourage your child to use decimal notation when counting money or measuring things around the house.
  • Play a game where you take turns making up decimal numbers and adding them together.
  • Use real-life situations like shopping or cooking to practice decimal addition and subtraction.
  • Ask your child to explain how they solved a decimal problem to make sure they understand the process.
  • Don’t worry if they make mistakes – they’re learning!
What to watch for:
  • Does your child line up the decimal points correctly when adding or subtracting?
  • Do they understand that 0.5 means 5 tenths and 0.25 means 25 hundredths?
  • Can they compare decimals correctly?

Practice questions

  1. What is 0.4 + 0.6?
  2. What is 1.25 + 2.75?
  3. What is 3.5 - 1.25?
  4. What is 0.8 - 0.3?
  5. What is 2.1 + 0.9?
  6. What is 4.25 - 1.75?
  7. What is 0.3 + 0.45?
  8. What is 1.5 + 0.25?
  9. What is 2.8 - 0.9?
  10. What is 0.75 + 0.25?
Answers:
  1. 1.0
  2. 4.00
  3. 2.25
  4. 0.5
  5. 3.0
  6. 2.50
  7. 0.75
  8. 1.75
  9. 1.9
  10. 1.00

FAQ

What are decimals used for in sailing?

Decimals are used in sailing to measure small distances, count money, and score points. For example, a distance might be 1.5 km, or a point score might be 0.75.

How do I add decimals?

Line up the decimal points and add the numbers like normal. For example, 1.25 + 2.75 = 4.00.

How do I subtract decimals?

Line up the decimal points and subtract the numbers like normal. For example, 3.50 - 1.25 = 2.25.

Why are decimals important?

Decimals help us measure and count small parts of things, like distances, money, and scores. They are used in many real-life situations.

How can I practice decimals at home?

You can practice decimals when shopping, cooking, or measuring things around the house. Try adding and subtracting prices or distances using decimals.