Question

The wheels of bicycles A and B have radii 30 cm and 40 cm, respectively. While traveling a certain distance, each wheel of A required 5000 more revolutions than each wheel of B. If bicycle B traveled this distance in 45 minutes, then its speed, in km per hour, was
1. 16π 
2. 14π
3. 18π
4. 12π

Answer 1

Correct Answer - Option 1 : 16π 

Calculation:

Let n be the number of revolution

Circumference of a circle → 1 revolution = 2πr

⇒ 1 revolution of wheel A = 2 × π × 30 = 60π cm

⇒ 1 revolution of wheel B = 2 × π × 40 = 80π cm

According to question

60π × (n + 5000) = 80π × n

⇒ 3n + 15000 = 4n

⇒ n = 15000

Distance = 20000 × 60π cm

⇒ Distance = (20000 × 60π)/(100000) km

⇒ Distance = 12π

Speed = (12π)/(3/4)

⇒ Speed = 16π

 ∴ The speed, in km per hour, was 16π.