# A city park contains a cylindrical artificial pond that has a radius of 7.5m. A 2m concrete deck will be constructed around the pond. The concrete should...............be at least 15 cm thick....

A city park contains a cylindrical artificial pond that has a radius of 7.5m. A 2m concrete deck will be constructed around the pond. The concrete should........

.......be at least 15 cm thick. Calculate the minimum volume of concrete required to construct the deck, to one decimal place?

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### 1 Answer

(1) The deck is 2m wide, and encompasses a pond with radius 7.5m. The surface area of the deck is `pi(11.5)^2-pi(7.5)^2=76pi` .(Take the area of the pond and deck, and subtract the area of the pond.)

(2) The volume of concrete is found by `Ah` where `A` represents the area, and `h` the height or thickness. Here `A=76pi m^2` and `h=.15m`

So `V=76pi*.15=11.4pi~~35.8m^3`

**The required volume is approximately 35.8 cubic meters.**