it says one minus, or defect probability of one%, raised to the power of nine, which is about 91%., you notice here the power of the exponen, if i take just for the sake of illustration, if i take even the 99% probability of doing something correct and i have many, many steps, say for the sake of argument, i have 50 steps in the process, my probability of producing something correct at the end of the process, my process yield, is about 60%.