Question

At the park there is a pool shaped like a circle. A ring-shaped path goes around the pool. Its inner radius is 7 yd and its outer radius is 9 yd.We are going to give a new layer of coating to the path. If one gallon of coating can cover 5v * d ^ 2 how many gallons of coating do we need? Note that coating comes only by the gallon, so the number of gallons must be a whole number. (Use the value 3.14 for pi.)

Answer 1

`\begin{gathered} r=7yd \\ R=9yd \\ A=\pi(R^2-r^2) \\ A=\pi((9yd)^2-(7yd)^2) \\ A=100.5yd^2 \\ ratio=5yd^2/\text{gallon} \\ #\text{ gallon=}\frac{100.5yd^2}{5yd^2/\text{gallon}} \\ #\text{ gallon=20.1} \\ \text{21 gallons of coating are needed} \end{gathered}`