This graph was given, which describes the current through a resistor, as a function of the voltage.
Then, we were supposed to find the resistance of the resistor when 3V<V<5V.
But it changes throughout this range, doesn't it? Because in the answers (Mind you, this is the FINAL physics exam in the country), it says we were supposed to do: R=ΔV/ΔI, which I believe isn't correct when the line doesn't go through (0,0).
What do you think?