Customary length to a smaller unit

• The numbers in this set run from 2 to 40.
• Every problem in it will convert to a smaller unit.
• A careful solution takes 1 written step on average.
• The mistake this set invites most often, in 45% of the problems: going to a smaller unit gives more of them, so multiply by 3 rather than divide.
• Answers are a whole number.

Drawing 240 problems from this page produced 101 different ones, 42% — so a sheet of 20 will come back to a problem you have seen — there are only so many sensible ones of this kind.