Plotting a roller coaster

Sorry byt there seems to be a circus tent on my graph...
and a roller coaster here...

The Circus is in Town!!!

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