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UKMT Senior Mathematical Challenge, 2024

Combinatorics Difficulty 2.0 Junior Find the answer United Kingdom

A bag contains four balls each of which is coloured either red or white. If one ball is drawn at random from the bag but not replaced and then a second ball is drawn at random, the probability that both balls are red is $\frac{1}{2}$ . What is the probability that both balls are white?

(A) $\frac{1}{2}$ (B) $\frac{1}{3}$ (C) $\frac{1}{4}$ (D) $\frac{1}{6}$ (E) $0$

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