James wants to build a 16-foot by 20-foot quilt. He uses patches that are each 4 square feet. The first 10 patches cost $10 each and then each patch after that cost half as much. How much do the patches for the quilt cost?
Thoughts? Step-by-step reasoning:
The patch is 16 * 20 = 320 square feet. So he needs 320 / 4 = 80 patches. The first 10 patches cost 10 * 10 = $100. He gets a discount on the next 80 - 10 = 70 patches. They each cost 10 / 2 = $5. So in total they cost 70 * 5 = $350. That means in total he paid 100 + 350 = $450.
Thus, the answer is 450.