Concrete forming tubes are used as molds for cylindrical concrete supports. the volume v of a tube is the product of its length l and the area a of its circular base. you can make 2/3 ft cubed of concrete per bag of cement. write a rule to find the number of bags of cement needed to fill a tube 4 ft. long as a function of its radius r. how many bags are needed to fill a tube with a 4-in. radius? a 5-inch radius?

Part A:

The volume of a cylinder is given by



where r is the radius of the base and h is the height.

Given that Concrete forming tubes are used as molds for cylindrical concrete supports. The volume of a tube 4 ft. long as a function of its radius r is given by



Given that 2/3 ft cubed of concrete can be made per bag of cement. Then the number of bags of cement needed to fill a tube 4 ft. long as a function of its radius r is given by:

bags of cement.

Thus, the number of bags that is needed to fill a tube with a 4-in. radius is given by



Part B:

Given that 2/3 ft cubed of concrete can be made per bag of cement. Then the number of bags of cement needed to fill a tube 4 ft. long as a function of its radius r is given by:

bags of cement.

Thus, the number of bags that is needed to fill a tube with a 5-in. radius is given by