Answer :
The probability of the event that the first digit is nine and the last letter is a is 1/260.
The building security code has 2 numeric digits in between 0-9 and 2 letters.
The choices for letters is 26 each and the choices for digits is 10 each.
So, the total possible security code can be,
Total security codes possible = 10 × 10 × 26 × 26
Total security codes possible = 67600
Now, the number of codes that starts with 9 and end with a are,
= 1 × 10 × 26 × 1
= 260
The probability that the first digit is nine and the last letter is a is,
P(E) = 260/67600
P(E) = 1/260
So, the probability that the first digit is nine and the last letter is a is 1/260.
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