A human adult breathes in approximately 0.50 L of air at 1 atm with each breath. If an air tank holds 10 L of air at 200 atm, how many breaths the tank will supply?

$p_{ 1 }$ $V_{ 1 }$ = $p_{ 2 }$ $V_{ 2 }$

===> 200 x 10 = 1 x $V_{ 2 }$

or $V_{ 2 }$ = 2000L

Therefore, number of breaths = 2000L/0.5 L

=4000