Final answer:
To calculate the number of spray paint cans John needs, first find the area of the circle with a radius of 4 feet and then divide by the coverage area of a can of paint. The area calculation is 16π and when divided by 20, John needs approximately 2.51 cans, which means he needs to buy 3 cans to have enough paint.
Step-by-step explanation:
John wants to spray paint the inside of a circle with a radius of 4 feet. To determine how many cans of spray paint he needs to buy, we must first calculate the area of the circle using the formula A = πr^2, where A is the area and r is the radius of the circle. John's circle has a radius (r) of 4 feet, so the area (A) is π × 4^2, which simplifies to 16π square feet. Since π is approximately 3.14159, the area can be calculated as approximately 50.27 square feet.
Each can of paint covers 20 square feet, so John will need to divide the total area of the circle by 20 square feet per can to find out how many cans are necessary:
50.27 sq ft / 20 sq ft per can ≈ 2.51 cans.
Since he cannot buy a fraction of a can, John will need to purchase 3 cans of spray paint to complete the job.