[sdiy] Calculating current out of a two resistor voltage divider?

[Justin Owen]

Ending the year on a big-hitter right...  :)

Seriously, I'm not near a breadboard or a multimeter, I have a bunch of schematics I'd like to try and understand, I wanted to analyse the current flow - but I'm second guessing myself as to how to calculate Iout...

http://www.sdiy.org/juz/voltage_divider_01.pdf

1) Iout = Vin/R1 (the same as if R2 was omitted)
2) Iout = Vout/R3||R4 (where R1 = R3 & R2 = R4) 
3) Something entirely different <inserting helpful answer here please...>

Thanks... again.

Happy New Year.

J