Area, Perimeter and Time: Year 4 Study Guide
Measurement helps us describe the size of real things and the time that things take.
Perimeter is the distance around the outside of a shape. Area is the amount of flat space inside a shape, measured in square units such as square centimetres (cm²). In Year 4, students measure area by counting unit squares and then use multiplication for rectangles: area = length × width.
They also read time on analogue and digital clocks, use 24-hour time and convert between units: 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day and 7 days in a week.
Perimeter and area of a rectangle
A rectangle 6 cm long and 4 cm wide has a perimeter of 6 + 4 + 6 + 4 = 20 cm and an area of 6 × 4 = 24 cm². Two shapes can have the same perimeter but different areas. A 5 by 5 square and a 2 by 8 rectangle both have perimeter 20 cm, but the areas are 25 cm² and 16 cm².
| Shape | Length × width | Perimeter | Area |
|---|---|---|---|
| A | 6 cm × 4 cm | 20 cm | 24 cm² |
| B | 5 cm × 5 cm | 20 cm | 25 cm² |
| C | 2 cm × 8 cm | 20 cm | 16 cm² |
24-hour time
The 12-hour clock uses am and pm. The 24-hour clock counts from 0000 (midnight) to 2359. For times after noon, add 12 to the hour: 3:30 pm is 1530. 8:15 am is 0815. 12 noon is 1200 and midnight is 0000. Timetables for trains and buses in Australia often use 24-hour time.
5:45 pm.
Add 12 to the hour.
1745.
Say it as 'seventeen forty-five'.
Time problems
Use a number line to find elapsed time. A film starts at 1:50 pm and ends at 3:35 pm: 10 minutes to 2:00, 1 hour to 3:00, 35 minutes to 3:35 gives 1 hour 45 minutes. Convert units: 2 hours is 120 minutes, and 180 seconds is 3 minutes.
Worked examples and common mistakes
Example: A floor 5 m by 3 m needs how many 1 m² tiles? 5 × 3 = 15. Common mistakes: adding only two sides for the perimeter, writing area in cm instead of cm², and subtracting times as if there were 100 minutes in an hour. Check by thinking whether the answer makes sense.
Check your understanding: model answers
1. Perimeter 20 cm; area 21 cm². 2. 2120. 3. 1 hour 35 minutes.
✨ Key Takeaways
- Perimeter is the distance around; area is the space inside.
- Area of a rectangle = length × width.
- 24-hour time: add 12 to pm hours.
- There are 60 minutes in an hour, not 100.
💬 Questions for Discussion & Reflection
- Find the perimeter and area of a rectangle 7 cm by 3 cm.
- Write 9:20 pm in 24-hour time.
- How long is it from 2:40 pm to 4:15 pm?