Barrels Full of Pellets - Solution
by
Erik Oosterwal
Number the barrels 1 - 10, then take 1 pellet out of barrel 1, 2 pellets
out of barrel 2, 3 pellets out of barrel 3, and so on for all 10 barrels.
If all 10 barrels would have had 1 gram pellets, the total weight of
the pellets should have been 55 grams. We're told, however, that 1
barrel has 2 gram pellets. If the 2 gram pellets are in barrel number
1, then the total weight will be 56 grams (1 more than we'd normally expect).
If the 2 gram pellets are in barrel number 2, the total weight wil
be 57 grams (2 more than we'd normally expect). What ever the total
weight is, subtract the expected number (55) from it and what ever numebr
you're left with, that's the barrel that has the 2 gram pellets.
Now that you know which barrel has the 2 gram pellets, the hard part of the
problem begins.
The real trick is to figure out which of the pellets in the pile go back
into which barrel, since you were only allowed to use the scale once and
you lacked the foresight to somehow label the pellets to indicate which barrel
they came out of.
This leads to an even trickier dilemma: If you were not the first person
to weigh the pellets, how can you be sure that the people who weighed them
before put them back in the correct barrels? Think about that one...
Discuss this and other logic puzzles here.
All original puzzles and solutions are © Erik Oosterwal 1993-2008
See all the brain teasers on The Puzzle Page.
Get daily puzzles in your RSS reader at The Puzzle Page Blog Site.
Looking for answers to computer programming problems?
Read what's going on in the Computer Science 101 classroom.