Simple parallel circuit problem

[Garth Wilson]

Often overlooked, and I don't know why since this is what's happening: Add the conductances, then invert again to get resistance:

a // b = 1/ (1/a + 1/b)

To do several at once do for example (in HP-41 programming):

Code:

100   \ First resistor value
1/X
330   \ Second resistor value
1/X
+
910   \ Third resistor value
1/X
+
[...] \ Go as far as you want.
1/X   \ Turn the sum of the conductances into resistance.

Doing it in complex numbers, it works for admittance too, ie, where there may be capacitive or inductive reactances.