@CPhill

a/.2

or

1/.2=2

it might be either of these depending on what you meant. I didn't understand if you meant a dollars as in a is a variable, or as a dollars as in 1 dollar.

If you meant a as a variable it is a/.2. 

if you meant a as in 1 it is 1/.2=2

Hope this helped!

That doesn't seem right... why would it be 5a? I think it is either $1.25 or \(\frac{5a}{4}\)dollars. A 20% disount reduces the price to 80% of the original cost, not 20%!

Let P be the original price

So...taking 20% off = .20P

So

P  - .20P  = "a"

P ( 1 - .20)  =  "a"

P (.80)  = "a"      divide both sides by .80

P  = "a"  /  .80