This puzzle is rated 2 stars (medium).
Four coins are laid out in a row, all with the "heads" showing.
You take any 3 coins and flip them over, so that 1 coin remains with the "heads" showing and 3 now have the "tails" showing. This is classed as turn number 1.
Making sure that you always flip exactly 3 coins each turn, how many turns in total (including the one completed in the description) will it take to have all the coins showing their "tails"?
Check the solutions page for the correct answer.