Q1. What is the area of a semicircle with radius seven centimetres?
✔ Area is half of pi r squared. Half times three point one four two eight five seven times forty nine equals seventy six point nine three.
Q2. Find the perimeter of a quadrant with radius five metres.
✔ Perimeter is quarter circumference plus two radii. Quarter of thirty one point four two plus ten equals twenty five point seven one.
Q3. Wei Ming tiles a semicircular floor at cost of two dollars per square metre.
✔ Radius is seven metres. Area is seventy six point nine three square metres. Cost is area times two dollars per square metre.
Show transcript
[Slide 1] Introduction to Parts of Circles
Hello class! Think about sharing a pizza at a hawker centre. We often cut it into halves or quarters. Today we calculate area and perimeter for these shapes.
[Slide 2] Formulas for Area and Perimeter
Remember, area is just half or a quarter of the whole circle formula. But for perimeter, do not forget to add the straight diameter line. Always check the boundary.
[Slide 3] Worked Example: Siti's Garden
Siti wants to fence her garden with radius four metres. We use the bar model to show curved part plus straight edge. Curved part is half circumference, straight part is diameter.
[Slide 4] Common Mistake Alert
A common mistake is calculating only the curved arc length. Always check if the shape includes the straight edge closing it. Do not miss the diameter.
[Slide 5] Recap and Practice
To recap, area is part of pi r squared. Perimeter is arc plus diameter. Now you can solve PSLE questions confidently.