Friday, September 21, 2007

How To Calculate a Percentage %

Why is it that Maths students, even those doing Further Maths, can never calculate a %? Every year I realise that very few students know how to calculate a %. Maybe it is not on the A Level maths syllabus?

% are one of the few maths learning of great practical use. When shopping, you won't have to differentiate a complex equation, but, you may need to work out the 20% discount of a good costing £40.

Anyway rant aside.

How to calculate a Percentage %

  • 20% of £40
  • 20% means 20/100. Therefore we multiply £40 * 20/100 = £8

20% 20/100 is the same as 0.2


  • If price increases from £40 to £44. What is the % increase?
  • We divide the difference (44-40) by the initial amount. * 100
  • Therefore it is 4 / 40 = 0.1
  • 0.1 * 100 = 10%

  • If price increases from 70 to 84. The % change is 14/70 *100 = 20%

If quantity was 3,000 and the Q.D increases by 20%. What is the new quantity?

we can times 3,000 * 120/100 = 3,600

Alternatively we can find 20% of 3,000 and then add it to 3,000

20% of 3,000 = 20/100 (0.2) * 3000 = 600

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8 comments:

  1. AnonymousApril 24, 2008 at 7:12 AM

    great! thnx .. for help.. :)

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  2. AnonymousSeptember 16, 2008 at 4:48 PM

    At last - found a decent page. You do this stuff in school, never use it till you start work. And you've already forgotten it. :)

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  3. suzeApril 15, 2009 at 12:11 PM

    Nice and simply explained! Perhaps it will stick now. If not will keep this page handy as a quick reminder. Why don't teachers make sure that children learn basics maths, such as this, ....because they don't! Could it be that the teachers don't know them themselves?!!? :)

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  4. suzeApril 15, 2009 at 12:20 PM

    Thanks for the nice simple explanation.... let's hope it sticks now.....never did at school; but then I went to 13 different ones and maths was taught differently at each - or so it seemed!.......It was all a bit of a mystery really. Perhaps that's why I only managed Maths 'O' level at age 37 before going on to study for two degrees!!

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  5. AnonymousMay 16, 2010 at 1:03 PM

    Not taught? This is GCSE stuff. You're pretty much expected to know this when doing your Year 11 GCSEs,so uhm,most A-Level students do know this. I'd know,considering I'm one of 'em.But there are quite a few people in my business class struggling with this so, great help for those who do need it.

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  6. PeriMarch 23, 2011 at 5:07 PM

    Thank you!! Very simple explanation out of all google web pages!!!

    ReplyDelete
  7. Jakk1974September 26, 2013 at 6:38 PM

    Thanks very much for your help. I'm 39 and still trying to work out how it works. This is the best tutorial by a mile. Now I'm free! !

    ReplyDelete
  8. AnonymousMarch 16, 2016 at 11:19 AM

    Thankyou for the help!!

    ReplyDelete