Think of Conductivity, instead.

Two parallel conductors will conduct better than one...

ConductivityTotal 
     = Conductivity(R1)
        + Conductivity(R2)
        + Conductivity(R3)
        + ....

Conductivity of a resistor = 1 / Resistance

WAY easier to remember, intuit, (and calculate?) than 1/Rt = 1/R1 + 1/R2 + 1/R3 ...