"Baldy" is correct also, the reciprocal method is also a way to solve for Rt. I find the above method easier than the reciprocal method when soloving for just two rersistors in parallel But the problem is, we were not solving for Rt. We are solving for Rx. I left that out thinking solving for an unknown (Rx) with algerba for guys who don't use it everyday would be trying. Maybe I should have pointed them in the direction of a "parallel resistance nomograph".
