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?

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 !!!