: Bridge Riddle : the answer
: The fastest way for the four people across is to group
similar speeds together.
; Here's the solution :
: Adam and Chivon cross with the lantern first. (2 minutes)
: Adam crosses back, bringing the lantern (1 minute, 3 mins total)
: Julio and Jenn cross, taking the lantern back (10 minuntes, 13 total)
: Chivon takes the lantern back to Adam (2 minutes, 15 total)
: Chivon and Adam recross, joining their friends (2 minutes, 17 total)
: The most common pitfall is to use Adam to ferry the
: across the bridge because his travel-time is the shortest. Unfortunately,
: this means that Adam crosses the bridge with each person, so we simply
: sum up the times (2 + 5 + 10) and add in Adam's two solo trips, giving
: 19 minutes total. Close, but no cigar.
: By having Julio and Jenn cross together, you essentially
re-coup 5 minutes
: of travel time, at the expense of having Chivon and Adam each cross
: extra time (3 minutes), for a net gain of 2 minutes.
: © 2001, Aaron Clauset
: Disclaimer: This puzzle is not of my devising. It was
one posed to me when
: I interviewed at Microsoft in the spring of 2001. Took me forever
to get the
: solution, because I got stuck in the 'common pitfall' explained above.
: once I got the solution, it was a great sense of achievement, because
: stuck so long :-)