Personal Comment: Easy if you are lucky at guessing.
Fill-in Multiplication Enigma
Story: Use the digits 1, 2, 3, 4, 5 and 6 once only, in this multiplication problem so that is it true:
(fill in a number for each of the "?")
? ?
x ?
___
? ? ?
Enigma:
Where can you put the numbers just once to have a true statement?