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Question 206901: Hello, I need help on one of my questions for summer. I did the rest im just stuck on this one, I really don't know how to do ratios. PLZ HELP!
okay so the question is:
According to the U.S Mint, pennies are made of 97.5 percent zinc and 2.5 percent copper by mass. Copper has a density of 8.96 grams of mass per cubic centimeter of volume. Zinc has a density of 7.13 grams of mass per cubic centimeter of volume.
A. What is the ratio of the mass of zinc to the mass of copper in a penny?
B. What is the ratio of the volume of zinc to the volume of copper in a penny?
C. You have measured the mass of some pennies that were minted before 1982, when they had a different composition than they do today. They were still made of zinc and copper, but in a different ratio. You have found that one penny has a mass of 3.1 grams, and has a volume of 0.35 cubic centimeters. Find the mass of the copper in this penny.
whoa!
Thank You SOO much!! If you could just help me with A and B i would probably be able to figure out the last one. Thank u thank u!
Answer by scott8148(6628)   (Show Source):
You can put this solution on YOUR website! A. "97.5 percent zinc and 2.5 percent copper by mass"
___ mass ratio is ... 97.5% : 2.5% ... or ... 39 : 1 ... or ... 39
B. density is the ratio of mass to volume ___ so to find volume; divide mass by density
___ using the result from A ___ volume ratio is ... (39 / 7.13) : (1 / 8.96) ... or ... 49.01 (approx)
C. (mass of copper) / (density of copper) = volume of copper
___ (mass of zinc) / (density of zinc) = volume of zinc
___ (volume of copper) + (volume of zinc) = .35
let x = "mass of copper" ___ (x / 8.96) + ((3.1 - x) / 7.13) = .35
multiplying by (8.96)(7.13) ___ 7.13x + 27.78 - 8.96x = 22.36 (approx)
-1.83x = -5.42 ___ x = 2.96 g (approx)
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