Circuit analysis

Hello board, I ran into a relatively (well I thought) simple problem, but I think I'm going brain dead.

**broken link removed**

The above circuit has a 100 ohm, and a 70 ohm(68 was closest) resistor in series with a resistor(Rx) in parallel across points A and B. There must be 3V at points A and B.

using ohms law

The series resistors must drop 17 volts

I = 17V/170ohms
I = 0.1 (100mA)

so Rx = 3/0.1 = 30 ohms?

Am I correct, please help

Thanks

You are correct as long as nothing is in parallel with the 30 ohm resistor.

Rx is not in parallel.
Rx is in series with the 100 ohm and the 68 ohm. You are correct that setting the value of Rx at 30 ohms will result in 3 volts across Rx.

Yes.

You can cross check by calculating the voltage across the 30 Ohm res.

V = 20 * 30/(30 + 170) = 20*30/200 = 3 Volt

QED.

By the way, Rx is not in parallel with anything. It is connected between points A & B.

Thank you all for your help, yeah I don't know what I was thinking, Just one of those days ;P

You're welcome. We all have days like that.