Maths Without Realising
Maths detective: setting a timer
A mini detective challenge where children spot time and subtraction while setting a timer.
Quick answer
Setting a timer helps you know when time is up, and you can use subtraction to find out how much time is left.Learning outcome
By the end of this page, you will be able to use a timer to track time and subtract to find how much time is left. Success signs:- You can set a timer for a specific amount of time
- You can tell how much time has passed
- You can subtract to find how much time is left
- You can use this in everyday life, like cooking or playing games
Why this matters
Setting a timer is like being a maths detective! You use maths to know when something starts and when it ends. When you set a timer for 10 minutes, you are using maths to count time. When you check how much time is left, you are using subtraction. This helps you with school tasks, games, cooking, and even sports. It's a super useful skill that you use every day!How it works
When you set a timer, you are choosing how long something should take. You can set it for minutes or seconds. Then, as time passes, you can check how much time is left. You can subtract the time that has passed from the total time to find how much time is left. For example:- Set a timer for 15 minutes
- After 5 minutes, you have 15 - 5 = 10 minutes left
- After 10 minutes, you have 15 - 10 = 5 minutes left
Examples you can see
Example 1: Cooking with a timer Imagine you are making pancakes. The recipe says to cook for 2 minutes. You set a timer for 2 minutes. After 1 minute, you check the timer and see 1 minute left. You subtract 1 from 2 to find out how much time is left. Example 2: Playing a game You are playing a game that lasts 10 minutes. You set a timer. After 3 minutes, you check the timer and see 7 minutes left. You subtract 3 from 10 to find how much time is left. Example 3: Getting ready for school You have 15 minutes to get ready for school. You set a timer for 15 minutes. After 8 minutes, you check the timer and see 7 minutes left. You subtract 8 from 15 to find how much time is left.Try it as a mini adventure
Adventure: The Great Timer Hunt You are a detective and your mission is to find the missing time in your house. You need to use timers to solve the mystery. 1st time: You find a timer set for 10 minutes. You check it after 3 minutes. How much time is left? (Answer: 10 - 3 = 7 minutes) 2nd time: You find a timer set for 12 minutes. You check it after 5 minutes. How much time is left? (Answer: 12 - 5 = 7 minutes) 3rd time: You find a timer set for 8 minutes. You check it after 2 minutes. How much time is left? (Answer: 8 - 2 = 6 minutes) 4th time: You find a timer set for 15 minutes. You check it after 10 minutes. How much time is left? (Answer: 15 - 10 = 5 minutes) 5th time: You find a timer set for 6 minutes. You check it after 4 minutes. How much time is left? (Answer: 6 - 4 = 2 minutes)Common mistakes
- Mistake: Thinking that the timer is wrong if it shows 5 minutes left after 5 minutes have passed.
Why it happens: Confusing the time that has passed with the time left.
Fix: Remember that if you set a timer for 10 minutes and 5 minutes have passed, then 5 minutes are left. The timer is correct! - Mistake: Not knowing how to subtract to find time left.
Why it happens: Not understanding that subtracting time that has passed from total time gives time left.
Fix: Use counting or drawing to help subtract. For example, if you have 12 minutes and 7 minutes have passed, count backwards from 12 to 7. - Mistake: Setting the timer for too long or too short.
Why it happens: Not thinking about how long something should take.
Fix: Think about how long a task takes before setting the timer. If you're brushing teeth, 2 minutes is good. If you're making a sandwich, 5 minutes might be enough.
Parent and carer guide
How to help your child:- Set a timer for simple tasks like brushing teeth or eating lunch
- Ask your child to check how much time is left
- Use subtraction to find out how much time is left
- Encourage your child to set timers for their own activities
- Play a game where you set a timer and see how many things they can do in that time
- "Let's set a timer for 5 minutes and see how much time is left"
- "How much time do you think it will take to finish this?"
- "Let's count backwards to see how much time is left"
- Your child might make mistakes at first. That's normal!
- They might not understand subtraction at first. That's okay. Use real objects to help
- They might set the timer too long or too short. That's part of learning!
Practice questions
- You set a timer for 10 minutes. After 3 minutes, how much time is left?
Answer: 10 - 3 = 7 minutes - You set a timer for 15 minutes. After 7 minutes, how much time is left?
Answer: 15 - 7 = 8 minutes - You set a timer for 8 minutes. After 2 minutes, how much time is left?
Answer: 8 - 2 = 6 minutes - You set a timer for 12 minutes. After 5 minutes, how much time is left?
Answer: 12 - 5 = 7 minutes - You set a timer for 6 minutes. After 4 minutes, how much time is left?
Answer: 6 - 4 = 2 minutes
FAQ
What is a timer?
A timer is a tool that helps you know when time is up. You can set it for a specific amount of time, like 5 minutes or 10 minutes.
How do I use a timer?
You set the timer for how long you want something to take. Then you watch the timer to see how much time is left.
Why do I need to subtract time?
Subtracting time helps you know how much time is left. It's like counting backwards from the total time.
Can I use a timer for anything?
Yes! You can use a timer for cooking, playing games, getting ready for school, or doing any task that takes a certain amount of time.
What if I make a mistake with the timer?
That's okay! You can always reset the timer or set it again. Making mistakes is part of learning.