On a tray there are 12 hard‑centred chocolates `(H)` and 8 soft‑centred chocolates `(S)`. Two chocolates are selected at random. A partially completed probability tree is shown.
What is the probability of selecting at least one soft-centred chocolate? (3 marks)
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`P(text{at least one}\ S)`
`= 1-P(HH)`
`= 1-(12/20 xx 11/19)`
`= 1-33/95`
`= 62/95`
♦ Mean mark 45%.