the mole fraction of h2 in a mixture of h2 and ch4 is same as the mole fraction of c2h6in a mixture of c2h6 and c3h8 containing equal weight of c2h6 and c3h8 calculate mole fraction of ch4 in the mixture of h2 and Ch4

Answer 1

The easy way of doing this is to assume a mass(any number will do as long as you make mass C2H6 the same as mass of CH8) for mass C2H6 and C3H8 and calculate XC2H6. To do this you have mols C2H6 and mols C3H8. Then XC2H6 - mols C2H6/total mols.
That becomes XH2 (the same number it says in the problem) and 1-XH2 = XCH4.