I got a question about those parallel resistors. When OP simplified them, he simply added the power of one resistor to the power of the other resistor. Is that correct way to do it for the parallel resistors?

If you have a resistor that is dissipating 100 W and another resistor that is dissipating 20 W and you put them into a black box, how much power is being dissipated by whatever is in that black box?

 

If you have a resistor that is dissipating 100 W and another resistor that is dissipating 20 W and you put them into a black box, how much power is being dissipated by whatever is in that black box?

Put that way, they will dissipate 120 W no matter how they are arranged.

 

Put that way, they will dissipate 120 W no matter how they are arranged.

Correct. Knowing that they are in parallel and how much each one dissipates allows us to determine the ratio of the two resistors.

 

I got a question about those parallel resistors. When OP simplified them, he simply added the power of one resistor to the power of the other resistor. Is that correct way to do it for the parallel resistors?

Yes you can, since the question never asks about the resistance. Of course, once you have the voltage across the pair, you can resolve the individual currents (and resistances).

Eric