Question 1074587
<pre>
We find the number of SUCCESSFUL ways, those which end in 3.
That will be the numerator of the probability:

Choose the most restrictive thing first.
That's the last or 4th digit 3.

Choose the 4th digit 1 way, as 3.
Choose the 1st digit any of the remaining 3 ways, as 1, 2 o 4.
Choose the 2nd digit either of the 2 remaining ways.
Choose the 3rd digit as the 1 remaining way.

Number of SUCCESSFUL identification numbers = 3×3×2×1 = 18

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We find the number of POSSIBLE ways, those with no restrictions
That will be the denominator of the probability:

Choose the 1st digit any of the 4 ways.
Choose the 2nd digit any of the 3 remaining ways.
Choose the 3rd digit as either of the 2 remaining ways.
Choose the 4th digit as the 1 remaining way.

Number of POSSIBLE identification numbers = 4×3×2×1 = 24

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The probability is 18 SUCCESSFUL ways out of 23 POSSIBLE ways.
"OUT OF" means "OVER" or "DIVIDED BY".

Probability of a SUCCESS = 18/24 which reduces to 3/4.

Edwin</pre>