A helium-filled balloon escapes a child's hand at sea level and 21.1 deg C. When it reaches an altitude of 3000 m, where the temperature is 4.8 deg C and the pressure is only 0.72 atm, how will its volume compare to that at sea level?

Well use the combines gas law to evaluate this question;

P₁V₁/T₁ = P₂V₂/T₂ (Remember that at sea level the pressure is usually 1 atm)

1 * V₁ / 294.25 = 0.72 * V₂ / 277.95 (NB: Temperatures have to be in Kelvin)

V₁ / 294.25 * 277.95 = 0.72 V₂

0.945 V₁ = 0.72 V₂

0.945/0.72 V₁ = V₂

1.312 V₁ = V₂

The volume (V2) at 3000 m altitude will be 1.312 bigger than the initial volume at sea level.