Answer to last riddle: Everyone on the bus was married, so not a "single" person was left on the bus.
Ah, a semantic riddle! I know I know, some of you feel cheated, heh. But a few of you still got it, so congrats! Let's try a mathy one as our next riddle. (I'm trying to mix up the flavours!)
Two trains speed toward each other on the same track. From 180 km apart, the westward train is travelling at a constant 120 km/h and the eastward train is travelling at a constant 150 km/h. A bee is hovering just on the nose of the westward train. It buzzes to the eastward train, turns around immediately, and flies back to the westward train. And on it goes, back and forth and back and forth until the trains crash and the bee is squashed to death. If the bee flies at exactly 300 km/h, what is the total distance that it flew?