**Circles calculate area circumference radius and diameter :**

Here we are going to see some example problems to understand how to calculate area and circumference of circle.

**Radius :**

The radius is a line segment with one end point at the centre and the other end on the circle. It is denoted by ‘r’.

**Diameter :**

Diameter is a chord passing through the centre of the circle. It is denoted by ‘d’.

The diameter is the longest chord. It is twice the radius.(i.e. d = 2r )

**Circumference of a circle:**

Can we find the distance covered by an athlete if he takes two rounds on a circular track. Since it is a circular track, we cannot use the ruler to find out the distance.

The distance around a circle is called the circumference of the circle, which is denoted by ‘C’. i.e., The perimeter of a circle is known as its circumference.

Circumference of circle = 2 π r

**Area of circle :**

The area of a circle is the number of square units inside that circle

Area of circle = π r²

**Example 1 :**

Find out the circumference of a circle whose diameter is 21 cm.

**Solution :**

**Diameter = 21 cm**

**Radius = 21/2 = 10.5 cm**

**Circumference of circle = **2 π r

= 2 (22/7) x 10.5

= 44 x 1.5

= 66 cm

Hence the circumference of circle is 66 cm.

**Example 2 :**

A wire of length 88 cm is bent as a circle. What is the radius of the circle.

**Solution :**

**Length of the wire = circumference of the circle**

2 π r = 88 cm

2 x (22/7) x r = 88

r = (88 x 7)/(2 x 22)

r = 14 cm

Hence the radius of the circle is 14 cm

**Example 3 :**

The diameter of a bicycle wheel is 63 cm. How much distance will it cover in 20 revolutions?

**Solution :**

When a wheel makes one complete revolutions,

Distance covered in one rotation = Circumference of wheel

Circumference of the wheel = 2πr units

= 2 x (22/7) x (63/2) cm

= 22 x 9 = 198 cm

For one revolution, the distance covered = 198 cm

For 20 revolutions, the distance covered = 20 × 198 cm

= 3960 cm

= 39 m 60 cm [100 cm = 1 m]

Hence the distance covered in 20 revolution is 39 m 60 cm

**Example 4 :**

A scooter wheel makes 50 revolutions to cover a distance of 8800 cm. Find the radius of the wheel.

**Solution :**

Distance travelled

= Number of revolutions/Circumference

2πr = 8800/50

2πr = 176

2 x (22/7) x r = 176

r = 176 x (7/22) x (1/2)

r = 28 cm

Hence the radius of the wheel is 28 cm

**Example 5 :**

The radius of a cart wheel is 70 cm. How many revolution does it make in travelling a distance of 132 m.

**Solution :**

Given: r = 70 cm, Distance travelled = 132 m.

Circumference of a cart wheel = 2πr

= 2 x (22/7) x 70

= 440 cm

Distance travelled

= Number of revolutions x Circumference

Number of revolutions

= Distance travelled/Circumference

= 132 m/440 cm

= 13200/440

= 30

Hence the number of revolution is 30.

After having gone through the stuff given above, we hope that the students would have understood "Circles calculate area circumference radius and diameter".

Apart from the stuff given above, if you want to know more about "Circles calculate area circumference radius and diameter", please click here

Apart from the stuff given in this section, if you need any other stuff in math, please use our google custom search here.

HTML Comment Box is loading comments...

**WORD PROBLEMS**

**HCF and LCM word problems**

**Word problems on simple equations **

**Word problems on linear equations **

**Word problems on quadratic equations**

**Area and perimeter word problems**

**Word problems on direct variation and inverse variation **

**Word problems on comparing rates**

**Converting customary units word problems **

**Converting metric units word problems**

**Word problems on simple interest**

**Word problems on compound interest**

**Word problems on types of angles **

**Complementary and supplementary angles word problems**

**Markup and markdown word problems **

**Word problems on mixed fractrions**

**One step equation word problems**

**Linear inequalities word problems**

**Ratio and proportion word problems**

**Word problems on sets and venn diagrams**

**Pythagorean theorem word problems**

**Percent of a number word problems**

**Word problems on constant speed**

**Word problems on average speed **

**Word problems on sum of the angles of a triangle is 180 degree**

**OTHER TOPICS **

**Time, speed and distance shortcuts**

**Ratio and proportion shortcuts**

**Domain and range of rational functions**

**Domain and range of rational functions with holes**

**Graphing rational functions with holes**

**Converting repeating decimals in to fractions**

**Decimal representation of rational numbers**

**Finding square root using long division**

**L.C.M method to solve time and work problems**

**Translating the word problems in to algebraic expressions**

**Remainder when 2 power 256 is divided by 17**

**Remainder when 17 power 23 is divided by 16**

**Sum of all three digit numbers divisible by 6**

**Sum of all three digit numbers divisible by 7**

**Sum of all three digit numbers divisible by 8**

**Sum of all three digit numbers formed using 1, 3, 4**

**Sum of all three four digit numbers formed with non zero digits**