Question

Andy wants to build a circular concrete patio in his backyard and install a jungle gym on top of it. One 80-lb bag of concrete will be enough for 2 square feet. If he wants the diameter of the patio to be 10 ft, how many bags of concrete will he need to purchase?

Answer 1

first thing you need to do is find the area of the circle A=(pi)r^2 You don't know r, but you do know the diameter is 10, and the diameter is twice the radius so r=5 Then plug that into the area formula, and you'll get A=25pi or 78.54 ft^2 If one bag covers 2 ft^2, then divide your area by 2 and round up to get the number of bags of concrete (40) 
hope i helped !!!