Train A takes 45 minutes more than train B to travel a distance of 450 km. Due to engine trouble, the speed of train B falls by a quarter and it takes 30 minutes more than Train A to complete the same journey. What is the speed of Train A (in km/hr)?

Solution : 

By ratio taking B 
B > S 4 : 3 
      T 3 : 4  > 4-3=1 = (45+30)=75min
       3=225 min 
Usual time => 225 + 45 = 270 min 

Speed of train A = 450/270 )*60 = 100km/Ans.