coverPlease do NOT post your answer, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.

I saw a friend of mine the other day.  When I asked him how old he was, he said, “In two years I will be twice as old as I was five years ago.” How old is he?
Oh, and just a quick reminder that I am at the Edinburgh Fringe Festival on Sunday.  Details here (use the code PSYCHOB001 to get a 20% discount).
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.

66 comments

  1. For the first time, I can honestly say that this took me less than a minute. Pen, paper, algebra. Tidy, as we say around these parts.

  2. well using algebra – the solution is trivial, but after doing that and rereading the puzzle, it came to me that carefully reading the puzzle, you can solve it rather simply in your head (i know you are still using algebra, but you can take a couple of shirtcuts, that makes it easy to solve in your head)

    1. yes, but by the time I’d worked out that I could have done it in my head, I’d done it on paper (and then run it past the question again to ensure I hadn’t missed anything). The number of times I’ve thought “I should be able to do this in my head” and spent ages getting my brain in a knot (or making educated guesses that are anything like) – or missing the question – I tend to go for paper at the first resort

    1. Hey John. I take you point. While an equation is strictly not an answer it near-as-dammit is. Just a trivial solving for x gives the answer. An answer is important, especially the correct one but the working is also important and that is what mittfh essentially gave out. The answer easily follows from that.

  3. Simple algebra. Less than a minute. I think even my 12 year-old brother could find out the solution to this one!

  4. Finally one I could solve!
    But then in seconds, not minutes.
    Is it really that easy, or have I missed something?

    1. Hi Deepfield (strangely where I live is called Deepfield), I think we had this ‘debate’ before whether a math’s problem is a puzzle or not. http://www.dictionary.com defines a puzzle as: “toy, problem, or other contrivance designed to amuse by presenting difficulties to be solved by ingenuity or patient effort.”. So a problem, maths or otherwise can be a puzzle.

  5. A very simple simultaneous equation. Even after 4 glasses of wine, it only took 4 seconds though I am prone to exaggerate by a factor of 4 when I have had 4 glasses of wine

    1. You’re probably wondering. I’ve now had 5 glasses of wine. By how much am I exaggerating? This is better than richard’s puzzle

    2. Hey Phil. “simultaneous equations” ? It’s not two equations in two unknowns but one equation in one unknown i.e. it’s not a simultaneous equation. Maybe the wine was making you see double ? Maybe you only drank 2 glasses of wine ?

    3. steve – as i ans’ed above, is two answers so must be simultaneous eqn. see previous above for more.

    4. Hi Dharmaruci. Mittfh gave one equation in one unknown above, which is what I had. I’d like to see your simultaneous equations for two solutions. Can you send to me via email ?

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