Question

The diameter of a cycle wheel is 21cm. How many revolutions many will it make to travel 1.98km

Answer 1

Radius of wheel= 21cm/2 = 10.5cm
therefore perimeter of circle=2 x 22/7 x 10.5cm= 66 cm

now perimeter of wheel= distance covered by it in single revolution.
therefore revolutions to be made by wheel to cover 1.98 km = 1.98km/66 cm 
= 198000cm/66cm= 3000                { 1.98km= (1.98 x 1000 x 100)cm}

hence the wheel will make 3000 revolutions to cover 1.98km. 

Circumference of wheel=πD=π21cm=65.97cm
The revolution it will take= 198000/65.77=3001.2