Let:
Mp = Marked price = $310
r = Rate of discount = 20% = 0.2
D = Discount
Sp = Sale price
The discount will be given by:
[tex]\begin{gathered} D=r\cdot Mp \\ D=0.2\cdot310 \\ D=62 \end{gathered}[/tex]And the sale price will be:
[tex]\begin{gathered} Sp=Mp-D \\ Sp=310-62 \\ Sp=248 \end{gathered}[/tex]