We are given a key pad assuming that the numbers are of 10 options from 0 to 9. IN thsi case, guessing the 3 digit pin number can be determined via counting method. The first number has 10 options so as second and third. Hence the total number of options is 10^3 or 1000. The probability of getting the pin teh first time is 1/1000 or 0.001.
