In a sale normal prices are reduced by 15% the sale price for cd player is £102 work out the normal price of the cd player

Ok, so the discount is given in a percentage, in this case 15%.  The sale price is going to reflect 15% of the original price minus the discount, so...

Sale £ = original£ - original£ x .15

If we use some algebra, we can reorganize the equation to solve for the original price...

Sale $ = original$ - original $ x .15
Sale $ = original$ (1 - .15)
Sale $ = original$ x .85
original$ = sale$/.85

So now we can plug in our values

original price = 102/.85
original price = £120