So if you had 6 computer chips 1-2-3-4-5-6 you could have 1-2, 1-3, 1-4, 1-5, 1-6, 2-1, 2-3, 2-4, 2-5, 2-6, 3-1, 3-2, 3-4, 3-5, 3-6, 4-1, 4-2, 4-3, 4-5, 4-6, 5-1, 5-2, 5-3, 5-4, 5-6, 6-1, 6-2, 6-3, 6-4, 6-5... <--all possible combinations = 30
(bold = defective computer chips)
out of those 30 combinations there is only 2 possibilities that both defective computer chips are chosen 2/30 (1-2 and 2-1)
there is 18 possibilities that only one defective computer chip is chosen 18/30
i hurt my brain doing this hope it helps ^-^
