Find impossible circuit resistance
Since you tend towards the correct answer as Rx tends towards 0 but clearly 0 is not a valid solution would Rx = 1/&#x221e; be considered an acceptable answer?

As has been said, not a good question. The only reason for it that I can think of is to drive home to the student that any additions to a circuit including instrumentation added in order to test or verify a circuit will have an impact on the circuit and the measured values. But there are better ways of doing that.