# Calculate Radius, Diameter, and Circumference

**Some useful relations:**

Diameter = 2 × radius

Circumference = 2 × π × radius

Also, circumference = π × diameter

Let's consider an **example **to look at the use of these relations.

Assume that the radius of a circle is 21 cm. Let's find the circumference of the circle.

Circumference = 2 × π × radius

= 2 × 3 × 21 [Using 3 as an estimated value for π]

= 6 × 21

= 126

So, the circumference of the circle is about **126 cm**.

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### Help

The correct answer is

##### Remember :

The smallest number is the one that comes first while counting.

##### Solution :

To arrange the given numbers in order from smallest to greatest, find the smallest number among all the given numbers.

21,27,23

21 is the smallest number.