1. **State the problem:** A chef bought 3 kilograms of flour on Monday and 4,000 grams on Friday. We need to find out on which day the chef bought more flour. 2. **Understand the units:** 1 kilogram (kg) = 1,000 grams (g). 3. **Convert kilograms to grams:** $$3\text{ kg} = 3 \times 1000 = 3000\text{ g}$$ 4. **Compare the amounts:** Monday: 3,000 g Friday: 4,000 g 5. **Conclusion:** Since 4,000 g > 3,000 g, the chef bought more flour on Friday. **Final answer:** The chef bought more flour on Friday.