Question

Please help me with this question​

Answer 1

`\mathrm{Let\ }(x+72)\ \mathrm{be\ the\ number\ of\ CDs\ and\ }x\ \mathrm{be\ the\ number\ of\ DVDs.}\\\mathrm{After\ selling\ 25\ percent\ of\ CDs,\ number\ of\ CDs\ is:}\\\\(x+72)-(25)/(100)*(x+72)\\\\=(x+72)-0.25(x+72)\\\\=x+72-0.25x-18\\\\=0.75x+54`

`\mathrm{After\ selling\ 40\ percent\ of\ DVDs,\ the\ number\ of\ DVDs\ is:}\\\\x-(40)/(100)* x\\\\=x-0.4x\\=0.6x`

`\mathrm{Now,\ after\ selling\ some\ CDs\ and\ DVDs,}\\\mathrm{Number\ of\ CDs=Number\ of\ DVDs+81}\\\mathrm{or,\ }0.75x+54=0.6x+81\\\mathrm{or,\ }0.75x-0.6x=81-54\\\mathrm{or,\ }0.15x=27\\\mathrm{or,\ }x=180`

`\mathrm{So\ initially,\ he\ had\ 180\ DVDs.}`