Wrong, But Useful: Episode 35

In this month's Wrong, But Useful, Dave and Colin discuss:

  • Colin gets his plug for Cracking Mathematics in early
  • Colin is upset by a missing apostrophe
  • Dave teases us with the number of the podcast and asks about the kinds of things it's reasonable to expect students to know, and asserts that the origin of the seven-day week is a quarter of the moon's cycle. Is that right?
  • So, 28 is the number of the podcast, although the sidereal month is 27.3 days.
  • We point out Big MathsJam conference, which (this year) is the weekend of the 12th-13th of November at Yarnfield Park, near Stone in Staffordshire. We discuss our past MathsJam experiences, which are uniformly positive, despite having to interact with each other in person.
  • Colin saw Colin Wright's juggling talk and recommends it.
  • Why are geometric progressions called geometric? Thanks to @sparksmaths (Ben in real life) for pointing Dave in the right direction.
  • @colinthemathmo asks: Is -3 a whole number? We argue. Is 0 a natural number? We agree, but are wrong (or possibly not).
  • @rjs2212, Robert in real life tweeted this:

    . Very neat!

  • Dave asks what happens when you work out Pascal's triangle modulo 9?
  • Dave is about to read What is the Name of This Book?
  • The last puzzle had a gold star for @dragondodo and a silver star for @chrishazell72 for having a pop.
  • Dave has a list of 24 numbers he needs to arrange into eight groups of three so that the totals are as even as possible. The numbers are:
    2, 2.29, 2.5, 2.5, 3, 3, 3, 3, 3.23, 3.23, 3.54, 4.17, 4.78, 4.78, 5.2, 5.52, 5.7, 6, 6, 6, 6.18, 7.5, 13, 14.06
    ... and the best solution is the one with the lowest standard deviation of totals.


Colin is a Weymouth maths tutor, author of several Maths For Dummies books and A-level maths guides. He started Flying Colours Maths in 2008. He lives with an espresso pot and nothing to prove.


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