Re-investment in buying a new machine/...finding mean?


New Member
Hi, I'm having trouble with this set up. I tried to use the normal distribution and calculate that cumulative distribution with 10% will occur for X<-1,27σ, but that did not really solve my problem. It could also be Poisson, but I always ended up stuck to an equation with two unknowns (mean and st. deviation). Could you guys please help me find a way?

"The manager of an engineering factory works on a new investment plan. The company recently bought a machine for cutting metal sheets. The guarantee is set up for one and half year. During this period, exactly 10 % of competitive companies complained to the distributor about this type of the machine. When should the manager expect the re-investment in buying a new machine again?"

Thank you very much.