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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.

51 comments

  1. 10 seconds of mental attempt before deciding to go for 20 seconds on paper. Then another 30 seconds deciding whether or not some might think this post is a spoiler. Which it isn’t. Or is it?

  2. Two pounds per day? Call the Union now. The Carpenter needs someone to fight for his right to be paid at least the National Minimum Wage!

    PS. It took about a minute. I could have done it quicker but my brain was still in “Union Leader on Holiday” mode.

    1. He would be better off with one of those new fangled zero hours contracts. I imagine he’s liberating the boss’s power tools, one piece at a time and it didn’t cost him a dime.

  3. Oh, that was an easy one… 5 seconds – but then I probably worked it out a different way from others. Will be good to see everyone’s working on Monday

  4. About half a minute or so using trial and error (although if I’d been thinking hard enough, I’m sure I could have used simultaneous equations).

    Even if this puzzle dates back several decades (when £2/day was equivalent to about £200/day), being fined time and a half for non-working suggests he’s being exploited. Being a carpenter, you’d expect him to have a decent grasp of mathematics, so perhaps there’s more to his contract than meets the eye? 🙂

  5. I think this depends on weather he works and/or is fined on weekends. Plus weather what day of the week the first monday of the month is, Without that knowledge, we cannot solve

    1. Thank you CTJ. That too.

      It is not enough that we make all the ass-u-me assumptions of what is in Richard’s mind when he wrote the Puzzle. We must root it in the real world for the benefit of those who solve it next.

    2. Or you could just read the fracking question and answer it Barry – or is that just too hard for you?

  6. I like Friday Puzzles… you keep practising simple simutaneous equations, and then you get the answer immediately thanks to Dave…
    Beware, Richard is watching us like lab rats. If not, he would easily be able to ban spoilers.

  7. 2x-3y=0, x+y=30, or y=30-x, so 2x-90-3x=0 5x=90 x=18, y=12 also, graphically, the 2 lines specified by the first 2 equations intersect at (18,12)

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