Please consider the attachment.
We have been given that 1 centimeter on the scale drawing represents 3 feet. We are asked to find the diameter of Clarise's fish pond.
We can see that radius of pond in 3 cm. We know that diameter is 2 times the radius, so diameter of the pond would be [tex]2\times 3=6[/tex] cm.
Now we will use proportions to solve our given problem.
[tex]\frac{\text{Actual length}}{\text{Scale length}}=\frac{\text{Actual diameter}}{\text{Scale diameter}}[/tex]
[tex]\frac{3\text{ ft}}{1\text{ cm}}=\frac{\text{Actual diameter}}{\text{6 cm}}[/tex]
[tex]\frac{3\text{ ft}}{1\text{ cm}} \times \text{6 cm}=\frac{\text{Actual diameter}}{\text{6 cm}} \times \text{6 cm}[/tex]
[tex]3\text{ ft}\times 6=\text{Actual diameter}[/tex]
[tex]18\text{ ft}=\text{Actual diameter}[/tex]
Therefore, the diameter of Clarise's fish pond is 18 ft.
