Rubidium exists as a mixture of two isotopes

CHEMISTRY · Subjective · A Level · Chemistry · Atomic structure · Atomic structure

Problem

Rubidium exists as a mixture of two isotopes,

{}^{85}\text{Rb}

and

{}^{87}\text{Rb}

. The percentage abundances are 72.1% and 27.9%, respectively. Calculate the relative atomic mass of rubidium.