Q1. What is the formula for circumference using radius?
✔ Radius must be doubled to find diameter before multiplying by pi.
Q2. Wei Ming has a plate with radius seven centimetres. What is the diameter?
✔ Diameter is always twice the length of the radius.
Q3. Cost to fence a circular garden with radius five metres at ten dollars per metre?
✔ Find circumference first, then multiply by the cost per metre.
Show transcript
[Slide 1] Understanding Circle Parts
Welcome class. Let us look at circles like MRT wheels or hawker plates. Remember radius goes from centre to edge, while diameter crosses the whole circle.
[Slide 2] Key Formulas for PSLE
To find the distance around, multiply pi by the diameter. If you have the radius, double it first to get the diameter. Always use 3.14 for calculations in exams.
[Slide 3] Worked Example at Tampines
Siti runs at Tampines Park. Imagine the radius as one bar model unit. The diameter is two units, and circumference wraps three times plus a bit. Calculate two times pi times fifty metres.
[Slide 4] Common Mistakes to Avoid
Many pupils forget to multiply radius by two. Always check if you are given the full width or half width. Ensure your final answer has correct metres or dollars.
[Slide 5] Quick Recap and Tips
Remember radius is half the diameter length. Circumference formulas depend on which part you know. Practice with local places like hawker centres to stay sharp.