After Hours

General discussion


Friday's Logic Puzzle

By cupcake ·
Tags: Off Topic
At the company I work, we have a Friday Quiz, in which the boss
sends out to his team a logic puzzle. There are specific rules and his
answer is the final answer. I felt that I answered the puzzle
successfully first, but he did not agree.

I am posting the puzzle (and the rules) here and I'd like to hear other's


Here are the rules for today (and they?re different from last time):

1. You may NOT use the Internet NOR may you ask for help from
anyone else; you MUST do your own work.

2. You may ask questions for clarification of the first two paragraphs
of the problem. However, I will only reply to questions that you have
asked by ?replying to all?. In other words, if you want to ask a
question, everyone gets to know the question; and when (if) I provide
an answer, everyone gets to know the answer too. When you have
your answer, submit that directly to me ? you don?t have to copy the
whole team on that one.

3. As usual, the question has been meticulously researched, although
the answer has not. Sticklers for the truth should start their own
game (although I don?t what you?d offer as a prize).

4. I will respond to emails in the order in which they are received.

5. Players who have won recently should sit on their hands and let
someone else have a chance for a change.

6. Ask as many questions for clarification as you want, BUT you may
submit ONLY ONE answer, and the first answer you submit is the one
I?ll go with, even if you submit a second, better answer later. You may
submit questions up until 10:30, and then I will answer all of them (in
other words, I have meetings until then). The game ends at 12:30 at
which time I will declare a winner.

So, here?s the problem for today:

You have 50 white marbles and 50 black marbles. You also have two
large opaque jars that rotate constantly. You may place any number
of marbles of either color in the jars in any fashion you want.

Once you have placed them to your satisfaction, I randomly determine
a jar, and randomly pick a marble from the jar. If the marble is white,
you win a prize. But, if it?s black . . . bad things happen.

So, how do you distribute the marbles between the two jars to
maximize you chance of winning? And, having done that, explain why
(bonus points if you can also give me the probability of winning based
on your solution).

This conversation is currently closed to new comments.

Thread display: Collapse - | Expand +

All Comments

Collapse -


by jck In reply to My thoughts

you think different than me.

it said "Once you have placed them to your satisfaction,...", I took that to mean all 100

Collapse -

The other 98

by TonytheTiger In reply to hmm...

were placed in his pocket :)

Collapse -

I see

by boxfiddler Moderator In reply to Friday's Logic Puzzle

your boss has borrowed some rules from Michael Feldman and the 'Whad'ya Know Show'.

Collapse -

I would have asked two questions and my answer would depend on those.

by ThumbsUp2 In reply to Friday's Logic Puzzle

(1) Must all 100 marbles be placed in one jar or the other?

(2) Can the Boss shake the jars before making the one marble selection?

If the answer to (1) is no, then the answer to (2) doesn't matter. Placing 1 white marble per jar would be the solution; chance of winning 100%.

If the answer to (1) is yes and the answer to (2) is no, then place 25 black marbles into each jar first; place 25 white marbles on top of them; chance of winning 100%

However, if the answers to (1) AND (2) are both yes and you put 50 marbles in each jar (25 of each color) and the jars can be "shuffled", your chances of winning drop to 50/50. This is where you might use the "winning" answer with 1 white marble in the first jar and the remaining 99 marbles in the 2nd jar. The odds on the first jar are 100%, but the odds on the 2nd jar are 49/50 making your overall odds roughly 75% chance of him grabbing a white marble, I think. Heck, I never have been good at odds!

Collapse -


by w2ktechman In reply to I would have asked two qu ...

I would have gone for clarification on 2 points. Do all of the marbles need to be added and how are the jars rotated

Collapse -

very simple

by jck In reply to Friday's Logic Puzzle

Put all the black marbles in one jar...then put all the white ones on top of them.

You have not said that the jar must have at least 1 marble.

Collapse -

What if

by NetMan1958 In reply to very simple

he reaches into the empty jar to pick a marble? No marble - you lose.

Collapse -


by Pringles86 In reply to What if

If he doesn't find a marble you don't lose. You don't win a prize, but you also don't have "bad things happen". It is sort of a draw.

Collapse -

Good point<nt>

by NetMan1958 In reply to No
Collapse -

it said

by jck In reply to What if

White Marble = prize
Black Marble = bad thing

If you write a program and say:


Do While WhiteMarbleCount < 50
If Marble = White then
WhiteMarblecount += 1
Elseif Marble = Black then
Output.write("Bad Thing")
BlackMarblecount += 1
End if
Output.Write("Your prize percent is " & _
(WhiteMarbleCount/(WhiteMarbleCount + BlackMarbleCount))*100
End Do


Notice, the game gave no condition for the Else in the rules of the game.

Hence, nothing occurs and they keep going until all 100 marbles are found...even if they reach in the empty jar.

Related Discussions

Related Forums