What is the Equivalent Resistance in this Circuit?

[keemosabi]

Homework Statement

http://img265.imageshack.us/img265/9245/45050879.png"

Homework Equations

The Attempt at a Solution

I really just don't know. I understand how equivalent resistance works, but I just don't get this question. Please ignore the marks I have on the page.

 

[rl.bhat]

Since the ammeter reads zero, that branch can be taken as short circuit or open circuit.
Now apply equivalent resistance formula to find R.

 

[keemosabi]

Since the ammeter reads zero, that branch can be taken as short circuit or open circuit.
Now apply equivalent resistance formula to find R.

Sorry, but I'm not really sure what you mean by that.

 

[rl.bhat]

Sorry, but I'm not really sure what you mean by that.

Have you heard about the Wheatstone Bridge? What is the balancing condition of the bridge?
When there is no current in the ammeter, either remove the ammeter from that branch, or replace it by a conductor and find the equivalent resistance of the circuit.