Navjivan Express from Ahmedabad to Chennai leaves Ahmedabad at 6.30 a.m. and travels at 50 kmph towards Baroda situated 100 km away. At 7.00 a.m. Howrah-Ahmedabad Express leaves Baroda towards Ahmedabad and travels at 40 kmph. At 7.30 a.m. Mr Shah, the traffic controller at Baroda realizes that both the trains are running on the same track. How much time does he have to avert a head-on collision between the two trains? Choose the correct choice from the following answers
A) 15 min  B) 20 min  C) 25 min  D) 30 min  E) 35 min
Explanation :   Let A be ahmedabad and B for baroda.   At 7:30 train from A to B would have covered 50km while train from B to A would have covered 20 km since it travels for only half an hour.   Distance remaining between the trains = 100-(50+20) i.e. 30km and the relative speed =90kmph. Therefore, time =30/90 hours = 20mins.   Answer : 20 min
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Navjivan Express from Ahmedabad to Chennai leaves Ahmedabad at 6.30 a.m. and travels at 50 kmph towards Baroda situated 100 km away. At 7.00 a.m. Howrah-Ahmedabad Express leaves Baroda towards Ahmedabad and travels at 40 kmph. At 7.30 a.m. Mr Shah, the traffic controller at Baroda realizes that both the trains are running on the same track. How much time does he have to avert a head-on collision between the two trains?