1. I need 6 quarts to change my oil but they sell only 5 quarts or 1 quart
2. 1 costs almost as much as 5 quarts
3. so you need to buy (2) 5 quarts, then you’re still short 2 quarts for the second oil change and buying (2) single quarts would cost as much as just buying a 3rd 5 quart
4. so you have to buy a 3rd 5, and it takes 5 oil changes to even out

5 oil changes and 25,000 miles to even to 0.