來價 ,標價 ,售價 ?

設來價為 z

z(1+30%)(1-20%) - z = $200
z(1.3)(0.8) - z = $200
z(1.04-1) = $200
z = $200 / 0.04
z = $5000

相機的來價為 $5000, 標價為 $5000 x 1.3 = $6500, 售價為$5000 + 200 = $5200

標價 = (1+30%) 來價
售價 = 80% 標價 = 80% [(1+30%) 來價] = 104% 來價
售價 - 來價 = $ 200
104% 來價 - 來價 = $ 200
4% 來價 = $ 200
來價 = $ 5000
標價 = (1+30%) $ 5000 = $ 6500
售價 = 104% $ 5000 = $ 5200

let x be the purchasing price
x (1 + 30%) is the mark price
x (1 + 30%)(1 - 20%) is the selling price
i.e. {x (1 + 30%)(1 - 20%)} - x = $200
1.04x - x = $200
0.04x = $200
x = $5000
thus, purchasing price = $5000
mark price = 5000 (1 + 30%) = $6500
selling price = 5000 (1 + 30%)(1 -20%) = $5200

設來價是y

y(1+30％)x0.8-y=200
0.04y=200
y=5000

來價是$5000
標價是$5000(1+30％)=$6500
售價是$6500(0.8)=$5200