$\log ( PV )=\log ( nRT )$

$\log P +\log V =\log n+\log R t$

Differentiate it

$\frac{\Delta P }{ P }+\frac{\Delta V }{ V }=\frac{\Delta n }{ n }+\frac{\Delta T }{ T }$

$\because$ It is filled in a rigid cylinder

$\Delta P =0$

$\frac{\Delta V }{ V } \times 100=-10$

$\frac{\Delta T }{ T } \times 100=20$

$\therefore-10=\frac{\Delta n }{ n } \times 100+20$

$\frac{\Delta n }{ n } \times 100=-30$

$\because n =\frac{ m }{ M }$

Where $m \rightarrow$ Mass of gas leaked

$M \rightarrow$ Molar mass

$\therefore \frac{\Delta m }{ m } \times 100=-30$

$\therefore 30 \%$ gas will leak out