Solving Nonideal Voltmeters with R_V, r, and E

[evilempire]

Here is the question, for reference:

A voltmeter with resistance R_V is connected across the terminals of a battery of emf E and internal resistance r. Find the potential difference Vmeter measured by the voltmeter.
Express your answer in terms of R_V, r, and E.

I have two equations but am having trouble solving them for V, clearly by eliminating I

E-(I*r)-(I*R_V)=0
V_ab=E-(I*R)

Any help would be appreciated, thanks.

 

[evilempire]

Nevermind, I got it, but the next problem is giving me a bit of trouble:

If E = 7.5 volts and r = .45 ohms, find the minimum value of the voltmeter resistance R_V for which the voltmeter reading is within 1.0% of the emf of the battery.

I am given the following equation to work with:

E(1-(r/(r+R_V))

 

[evilempire]

Nevermind, got that too. Disregard this thread, heh.