please help me step by step so i may understand this on how to put this together

Question

Copper (Cu) has two common isotopes. One isotope has 34 neutrons and 29 protons, and it accounts for 69.15% of all copper. The other isotope has 36 neutrons and 29 protons and it accounts for 30.85% of all copper. Using the isotopic composition provided, calculate the average atomic mass of copper. Round your answer to the tenths place.

Answer 1

First, add the protons and neutrons for each isotope to get the atomic mass.

Isotope 1:29+34= 63 amus

Isotope 2: 29+36= 65 amus

Second, multiply the atomic mass units by the % frequency in nature

63 amus*0.6915=43.56

65 amus*0.3085=20.05

Third, add them together

43.56 amus+ 20.05 amus=63.61 amus -->63.6 amus

Answer 2

(.6915)(63) = 43.5645

(.3085)(65) = 20.0525

Sum these: 63.617

Consult with your teacher as to how to handle sig figs here..

Answer could be: 43.56 + 20.05 = 63.61 if sig figging to four digits after initial multiplication is desired.