1. The problem statement, all variables and given/known data http://img638.imageshack.us/img638/2421/screenshot20100807at012.png [Broken] 2. Relevant equations 3. The attempt at a solution For the ammeter resistance i chose to find the difference in the voltmeter reading in the two circuits. that difference is the p.d. across the ammeter, right? but i don't know which ammeter reading to use now. in fact i think i have been on the wrong track all along. perhaps someone can give some hint for me to get started?