Formula's:
Area of FULL circle = π × r x r
Area of semi-circle = (π x r x r) / 2
Circumference of FULL circle = 2πr
Circumference of semi-circle = (2πr) / 2
Area of FULL circle = π × r x r
Area of semi-circle = (π x r x r) / 2
Circumference of FULL circle = 2πr
Circumference of semi-circle = (2πr) / 2
1.The radius of the smaller circle is 3.5 cm. The radius of the larger circle is twice that of the smaller circle. Find the area of: (pi = 22/7)
i.) The big circle
ii.) The small circle
iii.) The shaded part
i.) The big circle
ii.) The small circle
iii.) The shaded part
i. 22/7 x 7 x 7
154 cm2
ii. 22/7 x 3.5 x 3.5
= 38.5 cm2
iii. Area big circle - area small circle
= 154 - 38.5
= 115.5 cm2
154 cm2
ii. 22/7 x 3.5 x 3.5
= 38.5 cm2
iii. Area big circle - area small circle
= 154 - 38.5
= 115.5 cm2
2.
A swimming has the shape of a semi-circle. If the straight side (diameter) is 14 meters, find the perimeter of the pool. [pi=(22/7)]
A swimming has the shape of a semi-circle. If the straight side (diameter) is 14 meters, find the perimeter of the pool. [pi=(22/7)]
C = 2πr
= 2 x 22/7 x 7
= 44cm
= 44 x 1/2 (semi circle)
= 22cm
22 + 14 = 36cm (remember to add the straight side)
= 2 x 22/7 x 7
= 44cm
= 44 x 1/2 (semi circle)
= 22cm
22 + 14 = 36cm (remember to add the straight side)
3.
The sides of the square piece of paper is 22 cm long. If a semi-circle was cut on one side, what is the area of the remaining piece of paper? [ pi = (22/7) ]
Area of square:
l x b = 22 x 22 = 484 cm2
Area semicircle:
22/7 x 11 x 11 = 380.26
380.26 x 1/2 = 190.13 cm2
Area square - area semi circle:
484 - 190.13 = 293.87 cm2
l x b = 22 x 22 = 484 cm2
Area semicircle:
22/7 x 11 x 11 = 380.26
380.26 x 1/2 = 190.13 cm2
Area square - area semi circle:
484 - 190.13 = 293.87 cm2
4.
The rectangle has length 20 cm and breadth 7 cm. Find the area of the shaded portion? [ pi = (22/7) ]
The rectangle has length 20 cm and breadth 7 cm. Find the area of the shaded portion? [ pi = (22/7) ]
Area rectangle:
l x b = 20 x 7 = 140 cm2
Area circle:
22/7 x 3.5 x 3.5
= 38.5 cm2
Area rectangle - area circle:
140 - 38.5 = 101.5 cm2
l x b = 20 x 7 = 140 cm2
Area circle:
22/7 x 3.5 x 3.5
= 38.5 cm2
Area rectangle - area circle:
140 - 38.5 = 101.5 cm2
5.
C is the centre of the larger semi-circle. The smaller semi-circle has a radius of 3 m. Find the perimeter of the shape shown in the diagram. (pi = 3.14)
C is the centre of the larger semi-circle. The smaller semi-circle has a radius of 3 m. Find the perimeter of the shape shown in the diagram. (pi = 3.14)
Perimeter (circumference) of larger semi circle:
2 x 3.14 x 6
= 37.68 cm
Perimeter (circumference) of smaller semi circle:
2 x 3.14 x 3
= 18.84 cm
Total perimeter = circumference of larger semicircle + circumference of smaller semicircle + the straight line to C.
= 37.68 + 18.84 + 6
= 62.52cm
2 x 3.14 x 6
= 37.68 cm
Perimeter (circumference) of smaller semi circle:
2 x 3.14 x 3
= 18.84 cm
Total perimeter = circumference of larger semicircle + circumference of smaller semicircle + the straight line to C.
= 37.68 + 18.84 + 6
= 62.52cm