How is it possible that meta xylene exists? Methyl group is ortho para directing so it should direct the
 second methyl group to ortho or para position giving rise to ortho or para xylene but how can meta xylene be formed?
Friedel Crafts alkylation of toluene is far less regioselective than you might think.
The meta-substituted products are thermodynamically favoured. At higher temperatures, the alkylation yields more 1,3-dialkyl substituted benzenes.
On a larger scale, Dimethylbenzenes are typically not synthesized by alkylation of toluene, but stem from catalytic reforming processes using alkanes as feedstock.