1973 AHSME Problems/Problem 23

Problem

There are two cards; one is red on both sides and the other is red on one side and blue on the other. The cards have the same probability (1/2) of being chosen, and one is chosen and placed on the table. If the upper side of the card on the table is red, then the probability that the under-side is also red is

$\textbf{(A)}\ \frac14 \qquad \textbf{(B)}\ \frac13 \qquad \textbf{(C)}\ \frac12 \qquad \textbf{(D)}\ \frac23 \qquad \textbf{(E)}\ \frac34$

Solution

There are three red faces, and two are on the card that is completely red, so our answer is $\frac{2}{3}$ , which is $\boxed{\textbf{(D)}}$ .

1973 AHSC (Problems • Answer Key • Resources)
Preceded by Problem 22	Followed by Problem 24
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1973 AHSME Problems/Problem 23

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