The circumference of a circle is 123.2 cm. Calculate :
(i) the radius of the circle in cm;
(ii) the area of the circle to the nearest cm²;
(iii) the effect on the area of the circle if the radius is doubled.

Question

The circumference of a circle is 123.2 cm. Calculate :
(i) the radius of the circle in cm;
(ii) the area of the circle to the nearest cm²;
(iii) the effect on the area of the circle if the radius is doubled.

KnowledgeBoat · Accepted Answer

Let the radius of circle be r cm. (i) Circumference of circle = 2πr ⇒ 123.2 = 2 × × r ⇒ r = ⇒ r = = 19.6 cm. Hence, radius of circle = 19.6 cm. (ii) Area of circle = πr2 = × (19.6)2 = × 19.6 × 19.6 = 22 × 2.8 × 19.6 = 1207.36 1207 cm2. Hence, area of circle = 1207 cm2. (iii) Area of circle = π(radius)2 If radius is double then it will become 2r. New area = π(2r)2 = π × 4r2 = 4 × πr2. Hence, new area becomes 4 times the old area.

Mathematics

The circumference of a circle is 123.2 cm. Calculate :
(i) the radius of the circle in cm;
(ii) the area of the circle to the nearest cm²;
(iii) the effect on the area of the circle if the radius is doubled.

Mensuration

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The area of a circle is 394.24 cm². Calculate :
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Mathematics

The circumference of a circle is 123.2 cm. Calculate :(i) the radius of the circle in cm;(ii) the area of the circle to the nearest cm2;(iii) the effect on the area of the circle if the radius is doubled.

Mensuration

Related Questions

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Find the length of a rope by which a cow must be tethered in order that it may be able to graze an area of 9856 m2.

The area of a circle is 394.24 cm2. Calculate :(i) the radius of the circle,(ii) the circumference of the circle.

The circumference of a circle is 123.2 cm. Calculate :
(i) the radius of the circle in cm;
(ii) the area of the circle to the nearest cm²;
(iii) the effect on the area of the circle if the radius is doubled.

Find the length of a rope by which a cow must be tethered in order that it may be able to graze an area of 9856 m².

The area of a circle is 394.24 cm². Calculate :
(i) the radius of the circle,
(ii) the circumference of the circle.