cardinals - Proving two sets are Equinumerous

Prove that $[0,1] \approx [0,a)$ where $a$ is a positive real number.

I know I need to fine a bijective function function between the two sets. The $a$ in the second set is throwing me off. Origninally I was thinking of doing $x=\frac{1}{a}$ that would get me $[0,x)$. But i am unsure if this is the correct route. Also how do I address the open interval on $a$ as oppose to a closed interval?