Find R3 for Max Power in Basic Circuit Question

[orangeincup]

Homework Statement

Find a resistance, RL, to replace R3, that will draw maximum power from the sources

Homework Equations

RL=RTH

The Attempt at a Solution

Am I correct in saying if I set R3 to be Rth of the whole circuit, it would draw maximum power?

I calculated based on that
1/(1/(120+680) +1/(820+330)) = 471.1 Ohm Rth

I am not sure if I should have included the 100Ohm resistor(R3) in the calculation or not.

 

[NascentOxygen]

R₃ = R_th should work.

The 100Ω is not part of these calculations.

 

[orangeincup]

R₃ = R_th should work.

The 100Ω is not part of these calculations.

My book ssys the answer is 330Ohm, did I do the calculation wrong?

 

[NascentOxygen]

My book ssys the answer is 330Ohm, did I do the calculation wrong?

The Thévenin resistance is a little over 330Ω so looks like that's the approach they intend.

Determine the Thévenin resistance of each source, then these are added in series.