calculating percentages

[Explorer-8]

Is there a general formula for calculating the answer to a question like this one?
If an item has been bought for £500 after a reduction of 60% on the original price, what was the original price?

[sandyRoe]

£500=40% of the original price. £500x 2.5= original price...£1250

[dr b]

so the general formula would be original price = discounted price/(1-reduction). or 1250 = 500/(1-0.6)

[RATTER15]

Cant you just add the (in this case) 60% back onto the reduced price or am I missing something here?

[Prudie]

Think of the original price as 100%

£500 is (100-60)% of the original = 40%

To get back to the original 100% you need to

(£500/40) X 100 = £1250

[4getmenot]

yer much easier how prudie does it

[dr b]

how can it be easier when it's exactly the same thing?

500 x 2.5 = 500/0.4 = (500/40)x100

The question asked for a general formula.

[4getmenot]

just easier. :-) not saying yours is wrong or different but I would do it prudies way thats all :-)

[Prudie]

It's fine dr b but the uninitiated might ask where you got the 2.5 from

[Prudie]

Apologies, that wasn't you

[wildwood]

With easy percentages like 40% where it is easy to divide the price, I tend to divide by [in this case] 4 and then multiply 10.

Completely unconventional and extremely politically incorrect, but it works for me.

[AlBags]

Easiest way is like 4Get does it ...


Let someone else do it! : )

x 4Get .. Good news on the job too x

[4getmenot]

exactly or just ask at counter how much it used to be :-) thanks al xx

[vascop]

so the general formula would be:
original price = discounted price x 100/(100-reduction%).

in this case=500 x 100/(100-60)=500 x 100/40=1250

[Explorer-8]

Thanks for your answers. That was an interesting discussion. It's given me something to think about.

[WhiteBears]

Prudie's theory is a lot easier to understand :-)

[cazzz1975]

cost (divided by) reduction (per cent) x 100 = full price

500 divided by 60 x 100 = £833

[WhiteBears]

so many waysof working out the answer and people understands it different way. i only understood prudies way, but i dont understand Sandy's way .. where did 2.5 come from?

[WhiteBears]

this is how i got taught at school, because we had to show how we worked it out in steps:

40% = £500

so will need to work out the remaining 60%

(i would break it down, 40% then 20%)

40% = £500 (you know that from the first question)

(20% remaining = half of 40% = £250)

20% = £250

so you add them all up

40% + 40% + 20% = 100%

£500 + £500 + £250 = £1250

[Prudie]

Well I can tell you 100% the answer is £1250.Try taking 60% off that and you will get £500.

People often forget that percentage increases and discounts refer to the original number not what they end up with.

[Explorer-8]

Using Vascop's general formula, I can make it even easier to remember by abbrevating some of the words so that OP = original price; RP = reduced price; R% = percentage reduction. This gives me OP = RP x (100/100-R%). I worked out that SandyRoe's number 2.5 comes from the specific question of the 60% reduction, so that is from the (100/100-R%) part of the equation, ie. (100/100-60) = (100/40) = (5/2) = 2.5.