3. How many 4 digit numbers can be made from the digits 1, 2, 4, 5 and 7 if a prime number must be the first digit and 4 must be the last digit and no digit can be repeated?
Unfortunately the circus invaded my work space. my apologies.
(actually I think the answer is 18, any readers care to check that for me?)
102 Combinatorial Problems
First digit must be 2, 5, or 7. Last must be 4. So we have (3) * 3P3 = 3 * 6 = 18. Yep.
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