In this case, the chance of founding defect is 10% which mean the chance of not founding defect would be 90%. At least one defect would be the opposite of "no defect at all". Since the probability to find a good product is 90%, the chance to found 10 good product would be 0.9^10.
Then the chance for at least one defect would be: 1- 0.9^10= 1- 0.3486784= 0.6513
