If only the % discounts are listed, and you have to calculate the final price, then they are both important!
20% off 1000 = 1000 - 200 = 800
15% off 800 = 800 - 120 = 680
26% off 680 (wait; I need my calculator!) = 680 - 176.80 = 503.20
Why didn't they just say 50% off in the beginning?