Answer:
Ok, so the discount is given in a percentage, in this case 10%. The sale price is going to reflect 10% of the original price minus the discount, so...
Sale $ = original$ - original $ x .10
If we use some algebra, we can reorganize the equation to solve for the original price...
Sale $ = original$ - original $ x .10
Sale $ = original$ (1 - .10)
Sale $ = original$ x .90
original$ = sale$/.90
So now we can plug in our values
original price = 50/.90
original price = 55.55555 = $55.55 to the nearest nickel
