Voltage divider

Two resistors, one output. The ratio sets the voltage; the sum sets how much current you burn holding it there.

Hitting a voltage you actually want

Give a target and this searches every pair of standard values whose total sits in a sensible range, then ranks them by how close they land.

Where dividers go wrong

A divider only holds its voltage when nothing draws current from the output. Anything you connect sits in parallel with R2 and pulls the voltage down — which is what the output impedance above is telling you. Keep the load at least ten times that figure, or use the divider to drive a buffer rather than a circuit.