Maths ( 20 point )!!!!!!!!!!!!

一店主以$1000購入10盒模型, 我想你打錯, 不是$1000購入1盒模型

(a)
10盒模型總售價 = $200/盒 乘 8盒 + $200/盒 乘 2盒 乘 (100 – x) /100

10盒模型總售價 = $1600 + $400 乘 (100 – x) /100

x 是折扣 (discount), 如果 x = 15, 15% off, 即是八五折 (減 15%)

(b)
總盈利百分數 = 90%
總成本 = $1000
90/100 = (總售價 - 總成本)/ 總成本 = 總利潤/總成本
90/100 = ($200/ 乘8 + $200 乘 2 乘(100- x)/100 - $1000)/$1000
900 = 1600 + 400 (100 – x)/100 - 1000
900 = 600 + 400 (100 – x)/100
900 – 600 = 400(100 – x)/100
30000 = 400(100- x)
30000/400 = 100 - x
75 = 100 – x
x = 100 – 75
x = 25

而餘下2盒則以25% 折扣出售(即是七五折, 25% off, 減 25%)

A) 200乘8+2 乘 200x%
B）200乘8+2乘200x%=1000乘(1+90%)
1600+400x%=1900
400x%=1900-1600
400x%=300
x%=300/400
x=3/4