Correct Answer - D
In `(1)/(2)` h train A will cover = 27 km
Distance between P and Q
`= (480 + 40 + 27)` km
= 27 + 520
= 547 km
Total time taken in given condition
`= ((1)/(2) + (13)/(3)) h = (29)/(6) h`
New time taken according to condition
`(547 + 2 xx 54)/((66-54))`
`= (655)/(12) h`
Required difference in time = `(655)/(12) - (29)/(6) = (597)/(12)`
= 49 hour 45 min.