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

8 comments:

wiq said...

great! thnx .. for help.. :)

Steve said...

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. :)

suze said...

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?!!? :)

suze said...

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!!

Anonymous said...

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.

Peri said...

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

Jakk1974 said...

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! !

Anonymous said...

Thankyou for the help!!