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[circuitlab]https://www.circuitlab.com/circuit/r8v246/divider/[/circuitlab]

Can anyone explain what I am doing wrong here?

I was expecting R3 to have 4.5 volts across it as?

Also what it the correct method for calculating series / parallel circuit combinations?

i can calculate series or pure parallel circuits but cannot find any information how to calculate mixed circuits?

I get 4.5V when I run it

calculate your parallels first so r10 andr13 above would become one 50 ohm resistance lets you and me call this "simplifing " the circuit

it is 4.5 V.. 100 ohm // 100 ohm = 50 ohm then its voltage divider circuit v(on one of the 50 ohms) = 9(50/(50+50)) = 4.5 V

if anything still not clear contact me .. enjoy..

The circuit was wrong apologies all resistors were mean't to be 100 ohms and the voltage at the split was 3V's after further research, for a voltage divider circuit with load then the maths is different which I still don't fully understand...

"for a voltage divider circuit with load"

The maths are the same.

You just have to see that it is a voltage divider with one value of resistor at the top and a different one at the bottom.

The top value is whatever the single resistor is. The bottom resistor value is calculated from the values of whatever the actual bottom two resistors are in parallel.

So if the top resistor is R1 and the bottom resistors are R2 and R3, then the top value is R1 and the effective bottom value is:

R2*R3/(R2+R3)

Thanks signality that makes much more sense when you visualize it that way and it wasn't obvious to me before even when I was learning network analysis.