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Use of equals sign

March 29, 2014

Here’s a picture from a high street shop.

20140329-195746.jpg
This is clearly wrong as those two things aren’t equal although I do understand the message they’re trying to get across. They’re trying to show that the new smaller can is still equivalent to the old, larger can. I don’t know whether I’m being overly fussy or if this is a sign of a misunderstanding.
One problem in maths is misuse of the equals sign. For example in finding the volume of a cuboid, a student might write:
5×3=15×4=60
Again, this isn’t right (5×3 is not equal to 60) and the equals sign is almost being used as a comma.
A better way of writing it would be:
5×3=15
15×4=60
Or even just
5x3x4=60

Anyway I’m interested in your views of just how acceptable the use of the equals sign is in the picture.

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10 Comments
  1. Poor use of the equals sign is my number 1 maths pet hate – specifically the “follow-on-equals”. Unfortunately for the advert 125≠250 under any circumstances, so the use of equals as-is is not a good one. If it was dressed up with a few words to give it context, then they would have an advert that read better (mathematically speaking anyway). Something along the lines of:
    “amount of deo in a new 125ml can = amount of deo in a new 250ml can”.

    • I also dislike the follow on equals.

      I don’t think there’s is worth saving by adding in words. It just gets clunky.

      • I agree – for the sake of the advert, too many words reduce the impact, but without them the maths doesn’t work. It would’ve been better if they just had the 2 cans and an equals between them, without any capacities written down but with “new” and “old” inside them instead.

      • Yes, I think that would have been better.
        Using the word ‘compressed’ somewhere may have helped.

  2. Is the graphic stating that the new formula lasts twice as long, so they should last equal amounts of time?

    I think they should have found a better way to show it.

    With regards to the other things mentioned, I started a blog earlier on a similar topic! Will tweet you link when it’s live.

  3. As commented above, the ad should say old to new; their usage is however far more acceptable than the pupil follow on version. I often say, “What you write needs to be mathematically true.”

    • I agree. No need for the word mathematically either.
      Just ‘what you write needs to be true’

      Although this is undermined by it not be penalised in mark schemes.

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