UPSC CAPF Assistant Commandant Model Paper 2

GIVEN:
Speed of A = 30 km/h
Speed of B = 45 km/h
CONCEPT:
Speed, time and distance
FORMULA USED:
Distance = Speed × Time
CALCULATION:
Let length of race = D km
Time taken by B to finish the race = (D/45) hours
Total distance covered by A = (D – 4) km
Time taken by A to cover ‘D – 4’ km = (D – 4)/30 = D/45
3D – 12 = 2D
⇒ D = 12
∴ Length of race = 12 km