A train leaves Delhi at 5 am and reaches Chandigarh at 9 am. Another train leaves Chandigarh at 6 am and reaches Delhi at 11 am. Both run at uniform speeds on parallel tracks. At what time will they meet?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 7:40 am
The distance is not given, so take a convenient value: the LCM of the two journey times, 4 h and 5 h, that is 20 units. The first train runs alone for one hour; after that the gap closes at the sum of the two speeds.
Speed of the Delhi train \(\displaystyle =\frac{20}{4}=5\) units per hour; speed of the Chandigarh train \(\displaystyle =\frac{20}{5}=4\) units per hour
By 6 am the Delhi train has covered 5 units, so the gap is \(20-5=15\) units
Time to close the gap \(\displaystyle =\frac{15}{5+4}=\frac{5}{3}\) hours \(=1\) hour 40 minutes
Meeting time \(=6\) am \(+\) 1 hour 40 minutes \(=7{:}40\) am