Output impedance of voltage divider?

When connecting a 10S LiPo (42V) to my ADC via a voltage divider, I began wondering how to calculate the output impedance of the divider.

^{simulate this circuit – Schematic created using CircuitLab}

For example, what is the output impedance of the above circuit?

(The ADC's specs recommend a signal impedance of 10kOhm or less, which I simply translated to 0.5mA @ Vcc=5V (worst case) and figured I'd be fine as long as the signal can source/sink more than 0.5mA. But that's not really 'calculating' the impedance...)

Answer

The output impedance is the equivalent of the two resistors in parallel.

If you are lazy, you can approximate this by taking just the lower-valued one, in this case the 5k.