Let the marked price be x.
Discount percent = Discount / Marked price x 100
20 = Discount/x x100
Discount = 20/100 x x = 1/5x
Also,
Discount = Marked price − Sale price
1/5x = x - Rs 1600
x - (1/5)x = Rs 1600
(4/5)x = Rs 1600
x = Rs ( 1600 x 5/4 ) = Rs 2000
Thus, the marked price was Rs 2000.