In a week, he orders 10 * 300 = <<10*300=3000>>3000 apples.
When 3/4 of the stock is sold, the total amount of apples sold becomes 3/4 * 3000 = <<3/4*3000=2250>>2250 apples.
The amount of apples remaining is 3000 - 2250 = <<3000-2250=750>>750 apples.
#### 750