src/Prices/PriceCalculator.cs

@@ -16,6 +16,6 @@ public static class PriceCalculator
             throw new ArgumentOutOfRangeException(nameof(discountPercent), "A discount is between 0 and 100 percent.");
         }
 
-        return price - discountPercent;
+        return price * (100m - discountPercent) / 100m;
     }
 }