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
1 comment:
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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