Question

500.0 mL of a gas is collected at 745.0 mm Hg. what what will the volume be at standard pressure

Answer 1

This is an application of Boyle's law:
P₁V₁ = P₂V₂. we don't have to convert volume and pressure to standard forms. we can even use the pressure with mmHg
1 atm = 760 mmHg 
V₂ = P₁V₁ / P₂ = 745 x 500 / 760 = 490 ml
Note that here we assume constant temperature