The average atomic mass of chromium

Chromium has four isotopes. You will check that their shares add up, find the average atomic mass, and pick out the most common isotope.

The idea. $\bar{A} = \dfrac{\sum \text{mass} \times \text{share}}{100}$, with the shares in percent.

Your tasks.

1. Set total to the sum of the four shares, in percent.
2. Set average to the average atomic mass, in u.
3. Set most_common to the mass of the most common isotope, in u.