A5-digit combination lock can be opened only if a correct combination of digits is chosen. find the probability of guessing the correct combination if:
a. no digit is repeated
b. digits can repeat and zero is not one of the digits in the combination

1) If digits can not repeat, the number of possible variations is 10x9x8x7x6 =30,240

And the probaility of guessing is 1 / 30240 =0.000033

2) If digits can repeat an zero is no one of the digits, the number of possible variations is 9x9x9x9x9 = 9^5 = 59,049.

The probaility of guessing is 1/59,049 = 0.000017