How many atoms?

Problem:

Find the number of particles in 15.4g of sodium when one mole has the mass of 23g

Solution:

One mole has mass 23g
15.4g has $\frac{15.4}{23} $ mole
One mole has $ 6.022 \times 10^23 $ atoms.
So we have $ \frac{15.4}{23} \times 6.022 \times 10^23 = 4.032 \times 10^23 $ atoms.