Answer:
Step-by-step explanation:
Let the internal resistance be r .
Since in open circuit the volt is 1.55 V , this will be the source voltage .
Source voltage = 1.55
If external resistance be R .
1.55 / (R + r ) = .500
R + r = 3.1 ohm
So sum of internal resistance and external resistance will be 3.1 ohm.