Question

A 5-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

Answer 1

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