MATHS 一問

Let $C be the cost,
marked price = C+120%
= C*220%
= 2.2C

sold at 20% discount
= 2.2C* (1-20%)
= 2.2*0.8C
= 1.76C

The sold price is 76% higher than cost

do you mean the precentage changes?
if yes,,so:

let the cost be y
y x (1+120%) = the marked price
the marked price x (1-20%) = sold price
y x (1+120%) x (1-20%) =sold price

*****
(new price-the cost)/the cost x100% = the precentage changes..
[(1+120%)(1-20%)y-y] x 100%
=(2.2x0.8y-y)/y x100%
=(1.76y-y)/y x100%
=(0.76y)/y x100%
=0.76x100%
=76%

so the precentage increases 76%

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if you are still not understand,, feel free to ask me =]