6.18 An arable farmer is thinking of sowing scientifically modified crops next year. She believes that if she did so her profits would be £75 000, compared to £50 000 if she sowed unmodified crops. A neighbouring farmer has made it clear that if his crops are contaminated he will demand compensation.

The arable farmer guesses that the probability of contamination to be 40 per cent. In the event that the neighbouring farmer claims compensation there is a 30 per cent chance that the arable farmer would have to pay

£25 000 in compensation and a 70 per cent chance she would have to pay £50 000 in compensation.

(a) Construct a decision tree and use it to advise the arable farmer.

(b) An expert puts the probability that there will be contamination of the crops of the neighbouring farmer at 60 per cent. Should the arable farmer change her strategy in the light of this information?