# What is the atomic mass of lithium if 7.42% of its atoms have the mass of 6.02amu and 92.58% of its atoms have the mass of 7.02amu?

Dec 28, 2015

$\text{6.9458 amu}$

#### Explanation:

Consider 10000 atoms of $\text{Li}$.

$742$ of them would have mass $6.02$.
$9258$ of them would have mass $7.02$.

Hence the total mass of these $\text{10000 Li}$ atoms would be

$\left(742 \times 6.02\right) + \left(9258 \times 7.02\right) = 69458$

$\therefore$ $\text{1 Li}$ atom on average would have mass of $\frac{69458}{10000} = \text{6.9458 amu}$.