The problem suggests equimolar amounts of the two gases, however their masses will differ since the molar mass is not the same.
PV=nRT
n=PV/RT, n=moles
molar mass=grams/mole
thus you have n x (Mhelium) and n x (Mmethane)=mass helium and methane respectively, where M=molar mass.
The ratio of masses turns out to be the ratio of molar masses.
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