Q:

A passenger train leaves Calcutta at 4 PM and travels at the rate of 30 kilometres an hour. The mail train leaves Calcutta at 9 PM and travels, on a parallel line of rails, at the rate of 45 km an hour, when will the second train overtake the first?

• 1
  10 hrs after the first train start
• 2
  12 hrs after the second train starts
• 3
  10 hrs after the second train starts
• 4
  12 hrs after the first train starts
• 5
  None of these