Riddles, brain puzzles and mathematical problems

[BAndrew]

Could you weigh 2a+3b+4c+5d+6e+7f+8g+9h+10i+11j

Then figure out what it would be if all gasses weighed the same.

Subtract that from the actual number, and from then on figure it out?

Of course. That's actually the solution! Congratulations!

NOTE: any combination of the form:
k*a + (k+1)*b + (k+2)*c + ... + (k+9)
would do (k >0 and is an integer)