384 Frequently Asked Questions In Quantitative Finance
Solution
The trick is to realize that there is more to the bulb
than light.
Step one: turn on lamps 1 and 2, and go and have
some coffee. Step two: turn off 1 and turn on 3, then
go quickly into the room and touch the lamp.
It is controlled by switch 1 if it is hot and dark, 2 if it is
hot and light, 3 if it cold and light, 4 if it cold and dark.
Turnover
In a dark room there is a table, and on this table there
are 52 cards, 19 face up, 33 face down. Your task is
to divide the cards into two groups, such that in each
group there must be the same number of face up cards.
You can’t switch on a light, ask a friend for help, all the
usual disalloweds. Is this even possible?
(Thanks to golftango and Bruno Dupire.)
Solution
An elegant lateral thinking puzzle, with a simple solution.
Moveany19 cards to one side and turn them all over.
Think about it!
The use of an odd number, 19 in this case, can be seen
as either a clue or as a red herring suggesting that the
task is impossible.
Muddy faces
A group of children are playing and some of them get
mud on their foreheads. A child cannot tell if he has
