How do you work out the total resistance of a parallel circuit when not all resistor values are known, and voltage is also unknown? Lets say R1 is 5 ohms and R2 is 1M ohm and R3, R4 and RT are unknown.

 

Is current or power available for either R1 or R2, and either R3, R4, or total circuit current or power?

If not, you wouldn't have enough information.