Navjivan Express from Ahmedabad to Chennai leaves Ahmedabad at 6:30 am and travels at 50kmph towards Baroda situated 100 km away. At 7.00 am Howrah-Ahmedabad Express leaves Baroda towards Ahmedabad and travels at 40 kmph. At 7:30 am Mr. Shah, the traffic controller at Baroda realizes that both trains are running on the same track. How much time does he have to avert a head-on collision between the two trains?

1) 15 min
2) 20 min
3) 25 min
4) 30 min
5) 35 min

• The distance between trains is 100kms, it is evident that at 7.30,Navjivan Express(NE) would have covered 50kms, while the HA express would have covered 20 kms. Thus the distance between the 2 trains would be 30 kms @ 7.30. Since their relative speed is 90 km/hr, the remaining distance of 30 kms would be covered in 1/3rd of an hour i.e. 20min. Option (2)
• 11 years agoHelpfull: Yes(3) No(0)
• just take lcm for both the speed
  1st train 50kmph
  2nd train 40kmph
  take LCM of 5 & 4 (Cancel the zeros of both)
  LCM=20
  ANS IS 20 MIN :)
  
  If u think this trick wont apply for all apply for various data
• 7 years agoHelpfull: Yes(0) No(0)
• At 7.30 am Navjivan Express is at 50 km from A at the same time, Howrah-Ahmedabad Express is at 20 km from B. hence distance between the trains at 7.30 am is 30 km. Relative speed = 50+40 =90 kmph. Hence time left = 30/90hr = 20min
• 6 years agoHelpfull: Yes(0) No(0)