Bunuel
A basket contains apples and oranges only. If 2 fruits are randomly selected from the basket one after another
without replacement, what is the probability that at least one of them is an apple?
(1) The number of oranges in the basket is twice the number of apples.
(2) If 2 fruits are randomly selected from the basket one after another
with replacement, the probability that at least one of them is an apple is 5/9.
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked.
C. BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient to answer the question asked.
D. EACH statement ALONE is sufficient to answer the question asked.
E. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.
The probability that at least one is an apple is the same as \(1 -\) the probability that neither are apples.
In other words, it's \(1 -\) the probability that both are oranges.
\(1-P(both oranges)\)
\(1-\frac{o}{o+a}*\frac{o-1}{o+a-1}\)
\(1-\frac{o(o-1)}{(o+a)(o+a-1)}\)
Statement 1We are told that \(o=2a\)
\(1-\frac{2a(2a-1)}{(2a+a)(2a+a-1)}\)
\(1-\frac{4a^2-2a}{(3a)(3a-1)}\)
\(1-\frac{4a^2-2a}{9a^2-3a}\)
\(1-\frac{2a(2a-1)}{3a(3a-1)}\)
\(1-\frac{2(2a-1)}{3(3a-1)}\)
However, since we don't know a, we cannot find the probability.
-> Statement 1 alone is not enough.
Statement 2If 2 fruits are randomly selected from the basket one after another
with replacement, the probability that at least one of them is an apple is 5/9
Once again, the probability here is (\(1 -\) the probability that both are oranges). However, there is replacement this time.
\(1-P(both orange) = \frac{5}{9}\)
\(P(both orange) = 1-\frac{5}{9}\)
\(P(both orange) = \frac{4}{9}\)
\(P(both orange) = \frac{4}{9}\)
This means that \((\frac{o}{o+a})^2 = \frac{4}{9}\)
\((\frac{o}{o+a}) = \frac{2}{3}\)
We now know the probabilty of selecting an orange in the first pick of the problem is \(\frac{2}{3}\) but we still don't know anything about the number of apples or oranges so we cannot find how many will be found without replacement.
-> Statement 2 alone is not enough.
Both statements together Statement 1 told us that \(o=2a\) and from statement 2, we found that \((\frac{o}{o+a}) = \frac{2}{3}\)
Rewritten, statement 2 gives us:
\(3o = 2(o+a)\)
\(3o = 2o+2a\)
\(o = 2a\)
This is not new information so both statements together will not help either.
The answer is
E. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.