Please do NOT post your answer, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.
A carpenter is paid 2 pounds for each day that he works and forfeits 3 pounds for each day that he doesn’t work. After 30 days he has paid out exactly as much as he has received. How many days did he work?
I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.