A train leaves station P at 6 AM and reaches station Q at 10 AM. At the same time, that is at 6 AM, another train leaves station Q and reaches station P at 9:30 AM. The two trains cross each other at

They cross at 7:52 AM.

Train from P takes 4 hours; train from Q takes 3.5 hours.

Their speeds are D/4 and 2D/7 of the distance.

Meeting time t: t(1/4 + 2/7) = 1, so t(15/28) = 1.

t = 28/15 hr = 1 hr 52 min, giving 7:52 AM.