What is the volume ratio of a helium balloon at different altitudes?

[wiggler115]

A child's helium-filled balloon escapes at sea level and 20.0°C. It reaches an altitude of 3330 m, where the temperature is 5.0°C and the pressure only 0.65 atm. What is the ratio of its volume at this altitude to its volume at sea level?

PV/T=PV/T


i got .94

 

[mgb_phys]

Did you take into account the drop in air pressure?
What will this do to the volume of the balloon

 

[turin]

Also, don't forget that the pressure inside the balloon gets a contribution from the tension in the rubber.