Tricky riddles

A man hijacks an aeroplane transporting both passengers and valuable cargo. After taking the cargo, the man demands two parachutes, puts one of them on, and jumps, leaving the other behind. Why did he want two?

What rock group has four men that don't sing?

A train leaves from Halifax, Nova Scotia heading towards Vancouver, British Columbia at 120 km/h. Three hours later, a train leaves Vancouver heading towards Halifax at 180 km/h. Assume there's exactly 6000 kilometers between Vancouver and Halifax. When they meet, which train is closer to Halifax?

What am I?

When can you add two to eleven and get one as the correct answer?

A boy fell off a 30 meter ladder but did not get hurt. Why not?

What goes up but never comes down?

You are in a cabin and it is pitch black. You have one match on you. Which do you light first, the newspaper, the lamp, the candle, or the fire?

Four children and their pet dog were walking under a small umbrella. But none of them became wet. How?

While I am in air, I am not in oxygen. I am also in water, but not in hydrogen. I am necessary in all animals, but you won't find me in the zoo. Look in all brains and you'll find me there too. What am I?