Red and Blue Marbles

4 stars

You have two jars, 50 red marbles and 50 blue marbles.


A jar will be picked at random, and then a marble will be picked from the jar.

Placing all the marbles in the jars, how can you maximize the chances of a red marble being picked?

What are the exact odds of getting a red marble using your scheme?



Put one red marble in one jar (A), and the remainder in the other jar (B).

If jar A is selected, you have 100% chance of selecting a red marble.

If jar B is selected, you have 49/99 chance of selecting a red marble.

With a 50% chance of selecting jar A and a 50% chance of selecting Jar B, the odds become 50% + 50%*49/99 = 74.7474% or 148/198



  • Moderate
  • Logic
  • Mathematical
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Put one red marble in one, no blue marbles. And put the fifty blue marbles at the bottom and the forty nin marbles at the top. 100% chance
- Thisisfuntocomment (26 Apr 2014)

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