A bag contains 4 balls. Two balls are drawn at random and are found to
be white. What is the probability that all balls are white.
(Here it is.)
The question was correctly (!) closed as being an exact duplicate of
one that had been asked
before. The original
querent reasoned thus:
the rest of the balls could be
- all white
- One of them white
- none of them white
So among the three above possibilities only one satisfies our
conditions so the probability is ⅓.
But it not even the options given. What's wrong with my work?
Nothing, sir or madam, nothing whatever. The only better response to
a question like this is to flip over the table.