A mine air sample contains CH$_4$, CO, H$_2$, N$_2$ and O$_2$. The mine air analysis using Haldane apparatus gives the following results expressed in percentage of total sample volume.

Total contraction after combustion : 10.0

CO$_2$ formed after combustion : 6.0

O$_2$ consumed in combustion : 9.5

The percentage of CH$_4$ in the sample analysed is ______.