Solids, flat shapes and position · Usually met around P1
Semicircles and quarter circles
A semicircle has one straight edge, a quarter circle two.
How to do it
Method
A semicircle has one straight edge, a quarter circle two
2 semicircles = 1 circle = 4 quarter circles
Another way
Cut a pizza
One cut through the middle: halves. A cross: quarters
In full
Fold a circle along a diameter (a straight line through the centre) and cut: you get 2 equal semicircles. Fold again and you get 4 equal quarter circles. A semicircle has one straight edge and one curved edge; a quarter circle has two straight edges and one curved edge, and the straight edges meet at the centre. 2 semicircles make a circle, 4 quarter circles make a circle too, and 2 quarter circles make a semicircle. To tell them apart, look at how many straight edges each piece has, then at its size. Or think of a pizza: one cut through the middle makes halves; a cross makes quarters.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
What shape is in the picture?
- A. A semicircle
- B. A quarter circle
- C. A square
- D. A circle
Choose the right answer
Show the answer and working
Answer: A. A semicircle
Count the straight edges: none is a circle, one is a semicircle, two with a curved edge is a quarter circle.
Example 2
Ka-yee has 20 equal quarter circles. How many whole circles can they make?
Show the answer and working
Answer: 5
4 quarter circles make 1 circle: 20 in fours make 5 circles.
Example 3
How many whole circles can 18 equal semicircles make?
Show the answer and working
Answer: 9
2 semicircles make 1 circle: 18 semicircles in twos make 9 circles.
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