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Bidmas (brackets; indices; divide/multiply; add/subtract)

  1. Aug 14, 2015 #1
    I've just come across an example of this on the following website; http://www.bbc.co.uk/education/guides/zqn3r82/revision/5

    The example was;

    [40 - (2+4^2)] x 2

    The site said that if there are two sets of brackets calculate the inside brackets first. I proceeded as follows;

    inside brackets; 2+4^2 = 2+ 4x4 = 2+16 = 18

    then the outer brackets; 40 - 18 = 22

    then the last part; 22 x 2 = 44

    But the site gave 8 as the answer. Any idea where I'm going wrong?
     
  2. jcsd
  3. Aug 14, 2015 #2

    Mark44

    Staff: Mentor

    The site is wrong.
    In the first step, they have [40 - 62] * 2. Here they have done the addition before dealing with the exponent. 2 + 42 = 2 + 16 = 18. Addition is at a lower precedence than exponents. At the site, they are evaluating the expression as if it were (2 + 4)2 rather than 2 + 42 as given in the problem.
     
  4. Aug 14, 2015 #3
    Thank you. So is my answer of 44 (and the route taken to get there) correct?
     
  5. Aug 14, 2015 #4

    Mark44

    Staff: Mentor

    Yes.
     
  6. Aug 14, 2015 #5

    SteamKing

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    The media is almost invariably horrible at dealing with things mathematical or even requiring the simplest facility in doing computations.
     
  7. Aug 14, 2015 #6

    SteamKing

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    The Beeb (or the Boob, in this case) evaluated (2+42) as if it were (2+4)2, which leads to the erroneous answer of 8.
     
  8. Aug 14, 2015 #7

    Mark44

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    What I said in post 2:
     
  9. Aug 14, 2015 #8

    SteamKing

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    Yep, Mark, yer right. I overlooked your post.
     
  10. Aug 15, 2015 #9
    Thanks.
     
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