A 3 L tank of helium gas has a pressure of 1.2 atm. At 37∘C, the gas has a pressure of 2.5 atm. What is the initial temperature?

Initial : P₁ = 1.2 atm, T₁ = ? K
Final : P₁ = 2.5 atom, T₂ = (273 + 37) K = 310 K

For a fixed amount of gas with constant volume : P₁/T₁ = P₂/T₂
Then, T₁ = T₂ × (P₁/P₂)

Initial temperature, T₁ = 310 × (2.5/1.2) K = 646 K = 373 K