Question

How many copper atoms are in a pure copper statue with a mass of 142kg

Answer 1

142 kg in grams:

1 kg ---------- 1000 g
142 kg -------- ?

142 x 1000 / 1 => 142000 g 

Atomic mass Cu =  63.54 a.m.u

Therefore:

63.54 g ------------ 6.02x10²³ atoms
142000 g --------- ??

142000 x ( 6.02x10²³) / 63.54 =

8.54.10²⁸ / 63.54 => 1.34.10²⁷ atoms of Cu