ABout Maths Percentage Problem

Mary sells an electric kettle at $600 and the profit per cent is 20%.
If she decreases the selling price by 55%, find her loss per cent.
The original cost of the electric kettle
= $600 / (1+20%)
= $600 / 120%
= $600 / 1.2
= $500
The new selling price
= $600 * (1-55%)
= $600 * 45%
= $600 * 0.45
= $270
The percentage of loss
= ($500-$270)/$500 * 100%
= 230/500 * 100%
= 46%
So her percentage of loss is 46%


2006-12-28 11:14:11 補充：
小小補充：計算百分比售價的常用公式有1. 當已知 $x 它 y% 後的售價，求 x 的方法為「新的售價 / y%」2. 當已知 $x 和要知道它的 y% 後售價，求新的售價的方法為「x * y%」此題目應用了 1 式。

Mary sells an electric kettle at $600 and the profit per cent is 20%.
600/(1+20%)
=600/120%
=600/1.2
=$500
If she decreases the selling price by 55%......
500*(1-55%)
=500*45%
=500*0.45
=$225

Her loss percent is:
(600-225)/600*100%
=375/600*100%
=0.625*100%
=62.5%

So the loss precent is 62.5%

let x be the cost of the electric kettle.

(1+20%)x = 600
1.2x = 600
x = 500

decreases the selling price by 55%,
the price = $600 X (1-55%)
= $600 X 0.45
= $270

her loss per cent = [(500-270)/500] X100%
= 46%