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Last Updated: Thursday, 21 July, 2005, 07:03 GMT 08:03 UK
Think of a number... think Johnny Ball
Johnny Ball
Johnny was also one of the original presenters on Play School
He started out as a Butlins Redcoat, but television presenter Johnny Ball has become a familiar face with programmes like Think of a Number.

His inimitable style has helped countless children develop an interest in science and maths.

  • Johnny Ball came into our studio to talk about his new book Think of a Number

    And, he set us a puzzle!

    If you missed the details you can click on the link below to see the puzzle again.

    And the answer is at the bottom of this page.

    Johnny said that his aim is to get children enthusiastic about maths and numbers for their own sake.

    I think we spend too much time worrying about kids and maths

    He feels that children will enjoy maths if we make it more fun and he advises parents to play maths games with their children, such as dominoes.

    Brain Teaser

    Here are the details of the maths puzzle set by Johnny Ball

    Three friends share a meal at a restaurant.

    The bill comes to 30

    They divide it equally, paying ten pounds each.

    But the waiter realises he's made a mistake and should have charged 25.

    He gives the friends five pounds back .

    They decide to take one pound each and give the waiter a 2 tip

    So, each person ends up paying 9 and the waiter keeps 2, making 29 in total.

    What happened to the missing 1?

    The Answer

    There is no missing pound.

    You don't add the 2 to the 27 they've paid because the 2 is already included in that 27 - The 2 features twice

    The actual sum is the 27 plus the 3 they got back, which brings you to the original 30.

    The premise of the question is false!

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    Try our brain teaser


    Johnny Ball



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