A sample of an element consists of two isotopes. The relative abundance of each isotope is
shown in the table.
What is the relative atomic mass of the element in this sample?

Answer:

2) E

Isotope 1
Total mass = 31 + 38 = 69 Percentage = 60%|
Isotope 1
Total mass 31 +40 71
Percentage = 40%
Relative atomic mass =
(69 x 60) + (71 x 40)
= 69.8
100