GeekDad Puzzle of the Week Solution: Bolder Boulder

Reading Time: 2 minutes

Lined up at the start of the 2012 Bolder Boulder 10k. Image: Flickr/ilovememphis cc license

I discovered yesterday evening that my kids are lightning fast — at least when chased with a lawnmower. So I have a strategy for next year’s Bolder Boulder 10k. With 50,000 runners, many absurdly dressed, and about 15 bands, I’m not sure anyone would even notice.

Alas, it’s too late for this year’s race, but the post mortem made for a kinda nifty puzzle. Here it was:

With 50k people, we started in waves, each two minutes later than the next. Being perhaps a bit less confident of being lightning fast, we started at the very back. Imagine waves started at 7:00am and that we started last at 9:00am. Every wave consisted of 500 runners. 1/20 ran 6-minute miles, 1/20 ran 7-minute miles, 1/20 ran 8-minute miles, etc. until 1/20 ran 25-minute miles. Image Leif and I (and Kristi with our four-year-old mostly on her shoulders) “ran” 18-minute miles.

How many people did we pass?

There are a couple ways to solve. I used brute force — a spreadsheet with runners’ finishing times, listed in minutes past 7:00am. As happens sometimes, there was just a touch of ambiguity in the puzzle. Did we start at the front or the back of our own wave? If we started at the front of our wave, we caught 2,100 people who started ahead of us; if we started at the back of our own wave (which was, in fact, the case…), we passed 2,275 total.I accepted both answers.

While the puzzle took some figuring, most people who entered figured correctly. (One error that popped up a couple times is failing to give the waves ahead a head start…)

And the winner of this week’s $50 ThinkGeek gift certificate, randomly drawn from the pool of correct entrants, is…I fear perhaps not a dad at all? Or perhaps it’s a dad named Katherine? In any case, congrats, Katherine! The rest of us can use the code GEEKDAD68JH to get $10 of a ThinkGeek order of $50.

Don’t forget to tune in on Monday when Judd comes correct with another installation of PotW!

Get the Official GeekDad Books!