When Sourav increases his speed from 20 Km/hr to 25 Km/hr, he takes one hour less than the usual time to cover a certain distance. What is the distance usually covered by him? Pick one:
A) 125 km
B) 100 km
C) 80 km
D) 120 km
E) 60 km

Rationale: detailed solution here , the distance travelled by sourav is constant in both the cases . so , 20 x t = 25 x ( t - 1 ) = d = ) 20 t = 25 t - 25 = ) 5 t = 25 = ) t = 5 hrs so , distance travelled = 20 x 5 = 100 km . correct answer b .
Answer: B