Question 15
Beaver City's park is a 16×16 grid with some trash cells. Lucy has robots whose square operating areas may be 1×1,2×2,4×4 or 8×8. Each robot can clean exactly one cell within its area. The areas must cover the whole park exactly: every cell covered, no overlaps. Black cells in the diagram contain trash. What is the minimum number of robots needed to clean all trash?
