How many US pennies make one pound of copper?

Answer 1

There is 2,5% copper in the penny (the rest is mostly zinc)

so you need 40 pounds of pennies to have one pound of copper.

Each penny weighs 0,080 troy ounces

40 pounds is 583,33 troy ounces (see why I like the metric system?)

583,3 / 0,8 = 7291.66...

About 7293 pennies (almost seventy three dollars in pennies)

(some will be used and have corroded if that makes a difference... I do not know)

Minor CorrectionRight, it's easier and more accurate in metric units.

US cents made after 1982 are metric and weigh 2.5 gm. 2.5% of that is copper, so each coin contains 0.025 X 2.5 gm = 0.0625 gm of copper.

There are approximately 453.6 gm in one pound so the equation is:

(1 penny / 0.0625 gm) X (453.6 gm / pound)

The grams cancel (remember dimensional analysis from algebra?) which leaves

(453.6 / 0.0625) X (pennies / pound)

or 7258.