Box $$\(A\)$$ contains 7 red balls and 1 blue ball. Box $$\(B\)$$ contains 9 red balls and 5 blue balls. A ball is chosen at random from box $$\(A\)$$ and placed in box $$\(B\)$$. A ball is then chosen at random from box $$\(B\)$$. The tree diagram below shows the possibilities for the colours of the balls chosen. Find the probability that the two balls chosen are not the same colour. ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................

Mathematics
IGCSE&ALevel
CAIE
Exam No:9709_m20_qp_52 Year:2020 Question No:6(b)

Answer:

\(\frac{7}{8} \times \frac{5}{15}+\frac{1}{8} \times \frac{9}{15}\)
\(=\frac{44}{120}\left[\frac{11}{30}\right.\) or \(\left.0.367\right]\)

Knowledge points:

5.3.2 use addition and multiplication of probabilities, as appropriate, in simple cases (Explicit use of the general formula is not required.)
5.3.4 calculate and use conditional probabilities in simple cases.

Solution:

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