How many atoms of copper are in a pure copper penny that weighs 2.15 g? (1 amu = 1.6605 10-24 g) ?

Solution hopes you will get it. If 1 AMU is equal to 1.6605x10^-24, divide 1 gram by the AMU to find how many atoms in 1 gram.

1 / (1.6605x10^-24) = 6.022282445 x 10^23 You can probably round to four decimal places, so you have 6.0222x10^23 atoms of copper in a gram.

Multiply that by 2.15, the number of grams in a penny (6.0222x10^23) x 2.15 = roughly 1.2948 x 10^24 atoms