A security consultant is recommending that one of his clients install a keypad with a certain number of distinct characters at the front and back door of his home. The keypad is designed so that each character is pressed once in a certain order. If the consultant advises that the probability of someone guessing the code in one attempt to be less than 0.01%0.01%, what is the minimum number of characters the keypad needs?
Please help me here?
What have you tried?