...said the man who could solve partial differential equations in his head.
Fun story about him: a couple of other scientists approached him with a mathematical puzzle:
There are 2 bikes, 120 miles apart. They are each traveling directly towards the other, each at 15 mph. There is a fly on the front tire of the first bike.
The instant the bikes start moving, the fly goes straight toward the second bike. And as soon as it reaches the second bike the fly turns around. And it keeps going until it gets squished between the two bikes’ front tires when they meet.
If the the fly travels at 5 mph, how far did the fly travel?
Our author thought for a few seconds and gave the answer.
The scientists replied “Correct. And I’m glad you took the short way, by figuring out how long the bikes would take meet, and then figure out how far a thing going 5 mph travels in that time. Most people try to solve it by doing the limiting case of the infinite series.”
Our author replied, puzzled, “What do you mean? I *did* solve the infinite series...”
A remarkable solution, given that the fly will be 40 miles behind the first bike (and never overtake him) when the two bikes collide.
The source below gives the initial distance between the bicycles as 20 miles, the speed of the bikes as 10 MPH and speed of the fly as 15 MPH. Other than that it was a great story!
It’s not a particularly hard series to sum, the difficulty is construction the series, figuring out which series to sum. In my form it’s sum (1/5)^n, n from one to infinity. Then you have to multiply by 60, 4 being a scale factor that falls out, and 15 being the speed of the fly.