The departmental photocopier has three parts A, Band C which can go wrong. The probability that A will fail during a copying session is 10-$. The probability that B will fail is 10-' if A fails and...

Extracted text: The departmental photocopier has three parts A, Band C which can go wrong. The probability that A will fail during a copying session is 10-$. The probability that B will fail is 10-' if A fails and 10-5 otherwise. The probability that C will fail is 10-' if B fails and 10-5 otherwise. The 'Call Engineer' sign lights up if two or three parts fail. If only two parts have failed I can repair the machine myself but if all three parts have failed my attempts will only make matters worse. If the 'Call Engineer' sign lights up and I am willing to run a risk of no greater than 1 per cent of making matters worse, should I try to repair the machine, and why?