Can someone help me as a am racking my brain. I have been given this question; Two oil pipes with circular cross-sections are subject to the constraint that the sum of their diameters is 1m. By using careful reasoning find the diameters that give the maximum and minimum possible combined cross-sectional areas. In each case give the combined crosssectional area. Which I am unsure of. I dont get how you can get a maximum and minimum of a circle diameter when the volume of material going through it is irrelevant. Any assistance would be greatly appreciated.