Extinction arithmetic

You will write functions for the share of a group among the extinct species, for the number of species lost in a century, and for the yearly loss of a model community.

The idea. A share is the part divided by the whole, times $100$. A rate for a century divides the species by the number of years and multiplies by $100$. If a fraction $f$ is left after $T$ years, the share lost each year is $100 \times (1 - f^{1/T})$.

Your tasks.

1. Finish share. It gives the per cent that part is of whole.
2. Finish per_century. It gives the species lost for each century.
3. Finish yearly_loss. It gives the per cent lost each year.