Prince William Helps Save The Lives Of Two Teen Girls

A Prince and a hero.

Prince William captained a helicopter that rescued two teenage girls who were swept out to sea off the coast of Wales on Thursday afternoon.

The Royal Air Force told the BBC that Capt. Will and his team were engaged in one of its "fastest and shortest" operations, and their rescue chopper arrived in 38 seconds to rescue two girls - 16 and 13. 

The girls had been enjoying some body-boarding in Wales, but ended up caught in a strong riptide that dragged the girls out into the sea."When I got to her, the elder girl was clearly exhausted and was going under the water for what was the very last time," Winchman, Master Aircrew Harry Harrison told the BBC of the rescue effort.

And it was a good thing that Prince William is such an excellent pilot. According to Master Aircrew Harrison, every second counted.

"This was one rescue where we truly did arrive in the nick of time and managed to save two young lives," he said.

Ants on a Stick

One hundred ants are dropped on a meter stick. Each ant is traveling either to the left or the right with constant speed 1 meter per minute. When two ants meet, they bounce off each other and reverse direction. When an ant reaches an end of the stick, it falls off.
At some point all the ants will have fallen off. The time at which this happens will depend on the initial configuration of the ants.

Question: over ALL possible initial configurations, what is the longest amount of time that you would need to wait to guarantee that the stick has no more ants?
Presentation Suggestions:
You might give this at the end of lecture one day and present the answer the following lecture.
The Math Behind the Fact:
The answer is 1 minute! While ants bouncing off each other seems difficult to keep track of, one key idea (fun fact!) makes it quite simple: two ants bouncing off each other is equivalent to two ants that pass through each other, in the sense that the positions of ants in each case are identical. So, you might as well think of all ants acting with independent motions. Viewed in this way, all ants fall off after traversing the length of the stick, i.e., the longest that you would need to wait to ensure that all ants are off is 1 minute.