We take in account the following formula tot determine the relative atomic mass:
Relative atomic mass = atomic mass of isotope (1) × abundance of isotope (1) +
atomic mass of isotope (2) × abundance of isotope (2) + ... and so on
For element Y we have:
Relative atomic mass of Y = 20 × 0.15 + 22 × 0.5 + 24 × 0.35 = 22.4
