Here let us say x is the regular price.
let there be discount of say "y".
Now we are given that there is 40% discount.
So sale price = regular price - discount
discount = y = 40 % of x = 0.4x
So sale price = x - 0.4x
subtracting we get,
sale price = 0.6x
Sale price = 0.6 * regular price