A 5-digit PIN code cannot begin with zero and the remaining digits have no restrictions. If repetition of digits is allowed, then what is the probability that the PIN code begins with a 7 and ends with an 8?

Answer 1

number of possible codes
= 9x10x10x10x10 = 90000

number starting with 7 and ending in 8
= 1x10x10x10x1 = 1000

prob(your event) = 1000/90000
= 1/90

Answer 2

A 4-digit pin code can begin with any number except 0,1 & 2. If repetition of the same
digit is allowed, the probability of a pin code begin with 5 and end with a 3 is?