Circumference of a circle = Diameter × pi
Circumference of a circle = 40 cm × 3.14
Circumference of the wheel = 125.6 cm
1 Km = 1000m
Circumference of the wheel × 1000m = The number of revolutions
125.6 × 1000m = 125600
The wheel would make 125600 revolutions if the bike travels 1 km.