The Delhi Express runs @ 144 kilometers per hours and it reaches destination 20 minute ahead of schedule. If it averages 100 km/hour, it reaches 24 minute behind schedule. What is the average speed it should maintain in order to reach the destination on schedule?	Choose the correct choice from the following options
A) 250
B) 240
C) 230
D) 245
E) 235

Rationale: if the destination is d kilometer and the speed in order to reach on schedule is s km / hour , the time taken to reach on schedule is d / s hours thus we get two equations : d / 144 = d / s - 1 / 3 and d / 100 = d / s + 2 / 5 and subtracting the first equation from the second we get : 44 d / 14400 = 11 / 15 thus d = 14400 x 11 / 44 x 15 = 240 answer : b
Answer: B