After assembling an order for 12 computer systems, the assembler noticed that an electronic component that was to have been installed was left over. The assembler then checked the 12 systems in order to find the system missing the component. Assume that he checks them in a random order.
(a) What is the probability that the first system the assembler checks is the system that is missing the component?
(b) What is the probability that the second system the assembler checks is missing the component, assuming that the first system he checked was OK?
(c) Explain why the answers to parts (a) and (b) are different.