let the weight of the second alloy be y convert the percentage to fraction, that is 10/100=0.1, 18/100=0.18, 13/100=0.13 Total weight if the mixture is 0.1 x 25+0.18y=0.13(25+y) 2.5+0.18y=3.25+0.13y like terms together 0.18y +0.13y = 3.25-2.5 0.05y=0.75 divide both side by 0.05 Y is therefore 15 pound of 18% copper is needed
The answer is D. 140 cm². I think the circumference of the balloon means the circumference of the biggest circle. So the 21=2πr². While the surface area of a sphere is S=4πr². So the S≈140 cm².
