\(A=\{\text{exactly 3 oranges}\}\\ B=\{\text{exactly 6 apples}\}\\ P[A \cup B] = P[A]+P[B] - P[A \cap B]\)
\(\text{The total number of possible arrangements is found from Stars and Bars }n=8,~k=3\\ N=\dbinom{n+k-1}{k-1} = \dbinom{8+3-1}{3-1} = 45\)
\( \text{To determine }P[A] \text{ we note that first we pick 3 oranges}\\ \text{We then fill the remaining 5 fruits from oranges or bananas.}\\ \text{There are }\dbinom{5+2-1}{2-1} = 6 \text{ ways of doing this, so}\\ P[A]=\dfrac{6}{45} = \dfrac{2}{15}\)
\(\text{Likewise }\\ P[B] = \dfrac{\dbinom{2+2-1}{2-1}}{45}=\dfrac{1}{15}\)
\(\text{Finally we see that }A \cap B = \emptyset \text{ so } P[A \cap B] = 0\\ P[A \cup B] = \dfrac{2}{15}+\dfrac{1}{15} = \dfrac{3}{15} = \dfrac{1}{5}\)
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