The purchase price is 250, and the selling price is 400. It's not a loss to make a discount of more than 6.25. The price is 6.25% off 400 dozen, and the actual price is 400*0.625=250, which is just equal to the purchase price. At this time, you won't lose money. When the discount is greater than 6.25, the selling price is greater than the buying price, and all profits are made.