If you can't afford the rent at a certain place on your income alone, and you pay 30% of the rent and your roomate pays 70% is it legal?

As long as the landlord gets 100% of what is listed on the lease signed both both tenants it doesn't make a difference, but the person paying the 70% will likely have issues with paying that much.

legal yes if your room mate agrees to paying more rent than you do !!!! buy the way who is the lease made out to , you or both !!! dont forget your roomie can leave when ever he wants cant he ..

Legal? Yes.  Wise? Only if you get it in writing, so the other roommate doesn't later sue for the other 20 percent to make it "half". Also, the landlord may still require everyone on the lease to prove that they can afford the entire rent, if that's their policy.

It's fine as long as you two are happy with such proportion.

Of course it's legal. You can split rent any way you and your roommate decide to split it. 

The manner in which you split rent with your roommate is up to you and there are no legal restrictions on how you choose to do it.

In your previous post your roommate moved out!

If you sign a joint contract with anyone you are both individually legally liable to pay 100% of the rent, the landlord doesn't care who pays what % just that 100% is paid AND it also means if one tenant leaves the other tenant still has to pay 100% of the rent

The landlord only cares that the rent is paid in full and in time each month.  He doesn't care how the tenants split the rent.

However the tenants decide to split the rent is legal. There are no laws that govern how people decide on their finances.

The landlord doesn't care what proportion each of you pay, as long as the rent is paid 100% in full each month.

If your roommate is ok with that