I am not sure why I am getting this wrong or what the right approach is.. The book answer is 9 and I got 8 machines for part a). Can someone explain how the book answer is 9? What I did was say that since the machine is only 95% reliable, each cycle is extended by 5% so instead of a cycle time being 5 mins it is 5.25 mins long..Did that for all the products and found how much time is in 8 hours for 250 days.
Part A would need $5\cdot 25\,000$ minutes machine time per year in total, parts B and C similarly. Add the three figures up and divide the sum by $0.95$ to account for down-time and by $0.97$ to account for scrap. You will arrive at $982094.41$ minutes envisaged machine time. Divide this by the number of minutes in a year ($120\,000$), and you obtain $8.184$. This shows that you need $9$ machines to be on the safe side.
Thereby the word "scrap" was interpreted as follows: $3\%$ of the produced pieces are faulty and have to be thrown away.