What decimal fraction of an hour is $30\text{minutes}$?

We know that $1\text{hour}=60\text{minutes}$.
To find the fraction of an hour that $30\text{minutes}$ represents:

$$\text{Fraction}=\frac{30\text{min}}{60\text{min}}$$

$$\text{Fraction}=\frac{1}{2}$$

In decimal form:

$$\frac{1}{2}=0.5$$