Answer: The equivalent expression is:
new price = s*0.8
Explanation:
When the original price of something is A, and we have X% off, the new price if that object will be:
New price = A - (X%/100%)*A
Like in this case, the original price is s, and the discount is 20%
Then the new price can be written as:
new price = s - (20%/100%)*s = s - 0.2*s = s*(1 - 0.2) = s*0.8
This is the equivalent expression we wanted to get.