This year, 40 students have each travelled by one or more of plane $$\((P)\)$$, train $$\((T)\)$$ or boat $$\((B)\)$$. 7 have travelled only by plane. 11 have travelled only by train. 9 have travelled only by boat. $$\[ \begin{aligned} &\mathrm{n}(P \cap T)=8 \\ &\mathrm{n}(B \cap T)=3 \\ &\mathrm{n}(B \cap P)=6 \end{aligned} \]$$ Two students are chosen at random from those who have travelled by train. Calculate the probability that they both have also travelled by plane. .............................................

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