it is important that its less than 2.5, because the question states that 'the sample size is chosen so that the chance of shutting down the machine unnecessarily is less than 2.5%'. So this means since you use z=2, the upper 2.5% will never cause the machine to shut down because it is at the upper end where the machine will never shut down. This is because when you think about p, you want the machine to be in the upper 2.5% because that means it is working to near perfect standard.for that sample proportion q was it even important that it was less than 2.5?? because every solution ive seen so far doesnt use that fact. i think the z score has to be greater than 2.