Time-travel maths quest: decimals

Quick answer

You can use decimals to measure time, money, and small parts of things. Decimals help you be more precise when counting, just like how a clock shows hours and minutes, or how a ruler shows centimetres and millimetres.

Learning outcome

By the end of this page, you will be able to use decimals to measure small parts of time, money, and distance – like knowing that 0.5 of an hour is 30 minutes, or that 0.25 of a pound is 25 pence.

• You can say what 0.1, 0.2, 0.5, and 0.25 mean in real life.
• You can compare decimals like 0.3 and 0.4.
• You can use decimals to solve time and money problems.
• You can see how decimals are used in clocks, calendars, and rulers.

Why this matters

Decimals help us be more accurate in everyday life. When you're cooking, you might need half a cup of sugar (0.5). When you're looking at a clock, you might see 3:30, which is 3 and a half hours. When you're shopping, you might pay 2.50 pounds. Decimals help you understand these small parts of numbers and make your life easier.

Learning about decimals also helps you in school. You'll use them in maths, science, and even art. Understanding decimals is like learning a secret code that helps you measure and count better!

How it works

Decimals are a way to show parts of a whole number. Think of a whole pizza – that's 1. If you eat half of it, you’ve eaten 0.5 of the pizza. If you eat a quarter, that’s 0.25.

When we write decimals, we use a point (called a decimal point) to separate the whole number from the part. For example:

• 0.1 means 1 tenth
• 0.25 means 25 hundredths
• 0.5 means 5 tenths

Here’s how to think about decimals:

1. 0.1 is like 1 part out of 10 equal parts
2. 0.25 is like 25 parts out of 100 equal parts
3. 0.5 is like 5 parts out of 10 equal parts

Decimals help us measure things more accurately, especially when we can’t count in whole numbers. For example, if you walk 1.5 metres, you’ve walked 1 metre and 50 centimetres.

Examples you can see

Let’s look at some real-life examples of decimals in action!

Example 1: Clocks and Time

On a clock, you can see time in decimals:

• 1:30 = 1 hour and 30 minutes = 1.5 hours
• 2:15 = 2 hours and 15 minutes = 2.25 hours
• 3:45 = 3 hours and 45 minutes = 3.75 hours

Example 2: Money

When you have money, you can use decimals:

• 50 pence = 0.50 pounds
• 25 pence = 0.25 pounds
• 10 pence = 0.10 pounds

Example 3: Rulers and Distance

A ruler shows centimetres and millimetres. If you measure something that is 1.5 cm, that means 1 cm and 5 mm.

Example 4: Football Scores

Imagine you’re watching a football match:

• Team A scores 2.5 goals (that’s 2 goals and a half goal)
• Team B scores 1.75 goals (that’s 1 goal and 75 hundredths of a goal)

Example 5: Cooking

When you’re cooking, you might need 0.5 of a cup of flour, or 0.25 of a teaspoon of salt.

Try it as a mini adventure

Imagine you’re on a time-travel adventure! You’ve landed in Ancient Egypt, and you need to measure the height of a pyramid. You have a rope and a ruler, but the ruler only shows centimetres. You need to measure to the nearest millimetre – which means you need to use decimals!

Here’s your quest:

1. First, you measure the pyramid’s base and find it is 12.5 metres wide.
2. Then, you measure the height and find it is 20.75 metres tall.
3. Next, you measure a small block and find it is 0.3 metres long.
4. Finally, you measure a piece of gold and find it weighs 0.875 kilograms.

Your job is to write down each measurement in full sentences. For example:

• The pyramid is 12.5 metres wide.
• The pyramid is 20.75 metres tall.
• The block is 0.3 metres long.
• The gold weighs 0.875 kilograms.

Can you solve this challenge? Try to write your own time-travel measurements!

Common mistakes

• Mistake: Thinking 0.5 is the same as 0.05
  Why it happens: Confusing tenths and hundredths
  Fix: Remember 0.5 means 5 parts out of 10, while 0.05 means 5 parts out of 100
• Mistake: Writing 0.1 as 1.0
  Why it happens: Mixing up where the decimal point goes
  Fix: 0.1 means one-tenth, not one whole
• Mistake: Adding decimals like 0.3 + 0.4 = 0.7
  Why it happens: Not understanding how to add decimal parts
  Fix: Add the tenths together: 3 + 4 = 7, so 0.3 + 0.4 = 0.7
• Mistake: Thinking 0.25 is bigger than 0.5
  Why it happens: Comparing the numbers without thinking about what they mean
  Fix: 0.25 = 25 hundredths, 0.5 = 50 hundredths, so 0.5 is bigger

Parent and carer guide

As a parent or carer, you can help your child learn about decimals by:

1. Using clocks and calendars at home to show how decimals work in time.
2. Shopping together and asking your child to find 0.5 of a pound or 0.25 of a pound.
3. Measuring things with rulers and talking about millimetres and centimetres.
4. Playing games like “Decimal Hunt” where you look for decimals in the house.
5. Practising with simple addition and subtraction of decimals, like 0.2 + 0.3 = 0.5.

Don’t worry if your child makes mistakes – they’re part of learning. Encourage them to think about what the decimal means, not just how to write it.

Practice questions

1. What is 0.5 of an hour in minutes?
2. How much is 0.25 of a pound in pence?
3. Write 0.75 as a fraction.
4. Which is bigger: 0.4 or 0.35?
5. What is 0.1 + 0.2?
6. How many millimetres are in 0.8 cm?
7. What is 0.5 of 10?
8. Write 0.25 as a percentage.
9. How much is 0.1 of 50?
10. Which is smaller: 0.1 or 0.01?

Answers:

1. 30 minutes
2. 25 pence
3. 3/4
4. 0.4
5. 0.3
6. 8 millimetres
7. 5
8. 25%
9. 5
10. 0.01

FAQ

What is a decimal?
A decimal is a way to show parts of a whole number, like 0.5 or 0.25. It uses a decimal point to separate the whole number from the part.

How do decimals work with time?
Decimals help us show time more precisely. For example, 1.5 hours means 1 hour and 30 minutes.

Why do we need decimals?
Decimals help us be more accurate when we can’t count in whole numbers. They are useful in money, time, and measuring things.

How can I practice decimals at home?
You can practice decimals by using clocks, rulers, shopping, or even cooking. Try asking your child to find 0.5 of something or to measure something in centimetres and millimetres.

What is the difference between 0.1 and 0.01?
0.1 means 1 part out of 10, while 0.01 means 1 part out of 100. So 0.1 is bigger than 0.01.