Question

if the circumference of a circle is 94.2 CM then its radius = ______ CM

if the circumference of a circle is 25.12 cm then it's radius = ______ CM ​

Answer 1

First we have to know the formula, so that we can find the answer easily.

The formula to be used in both the questions are same.

Formula :-

Circumference = π × diameter

Diameter = 2 × radius

Substituting the formula of diameter in circumference, we get

Circumference = 2 × π × radius

Solution :-

Solving the first Question.

1. Circumference = 94.2 cm

Taking π as 3.14

$=> Circumference = 2 × π × radius \\ \\ => radius =\frac{Circumference}{2 \times \pi} \\ \\ = > radius = \frac{94.2 \: cm }{2 \times 3.14} \\ \\ = > radius = \frac{30 \: cm}{2} \\ \\ = > radius =15 \: cm$

2. Circumference = 25.12 cm

Taking π as 3.14

$=> Circumference = 2 × π × radius \\ \\ => radius = \frac{Circumference}{2 \times \pi} \\ \\ = > radius = \frac{25.12 \: cm }{2 \times 3.14} \\ \\ = > radius = \frac{8 \: cm}{2} \\ \\ = > radius =4 \: cm$

Answer :-

1. Radius = 15cm

2. Radius = 4cm

Note :-

• Why I have taken π as 3.14 not 22/7. I have taken π as 3.14, so that the decimal part can easily be divided.

• It is also not mentioned in the question what value we have to take for pi.