Question

If the circumference of a circle is 31.4 cm, then find its radius.
Calculate the area of a circle whose radius is 0.8 cm.​

Answer 1

Explanation:

As we know that circumference of the circle is given as-

Circumference =2πr

Given:-

Circumference of the circle =31.4cm

∴2πr=31.4

⇒2×3.14×r=31.4

⇒r=5cm

Now again as we know that the area of the circle is given as-

Area =πr

2

⇒ Area =3.14×(25)

2

=78.5cm

2

Hence the radius and area of the circle is 5cm amd 78.5cm

2

respectively.

Answer 2

Answer:

$circumference \: of \: circle = 2\pi \: r \\ 31.4 = 2 \times \frac{22}{7} \times r \\ \frac{314 \times 7}{10 \times 2 \times 22} = r \\ 4.9 cm = r \\ area \: of \: circle = \pi \: {r}^{2} \\ = \frac{22}{7} \times {(0.8)}^{2} \\ = \frac{22}{7} \times 0.64 \\ = 2.01 \: {cm}^{2}$