Question

The diameter of the wheel of a car is 77 cm. How many revolution will it make to travel 121 km?

Answer 1

Diameter of the wheel = 77cm

So, we need to find the circumference of we need to solve this.

So, Circumference
$= \pi \: d \\ = \frac{22}{7} \times 77 \\ = 242cm$
Now, the distance needed to cover = 121 km
Now, notice that the distance is in km so we will convert km into cm.
121 km = 121000000 cm

Now, as both units are equal we can divide the distance by the circumference of the wheel to get the number of revolutions.
$= \frac{121000000}{242} \\ = 500000$
So, 500000 revolutions are needed for the wheel to cover a distance of 121 km.

Answer 2

SOLUTION :

The diameter of the wheel of car = 77 cm   (given)

To be found :-

The number of revolution the car will make to travel 121 km

radius of the wheel = 77 ÷ 2 = 38.5 cm   [ as radius = diameter ÷ 2 ]

1 revolution of the wheel = 1 circumference of the wheel

So,

Circumference of the wheel = 2πr  units

                                               = 2 × 22/7 × 38.5  cm

                                               = 242 cm

242 cm = 0.00242 km   [ ∴ As 1 km = 100000 cm ]

If the wheel makes 1 revolution to covers 0.00242 km

So,

The number of revolution the wheel will make to cover 121 km is

= $\frac{ \bf{121} }{ \bf{0.00242} }$

= 50000 revolutions

Hence

the wheel of the car will make 50000 revolutions to travel 121 km.