[LorentzForce]

Hey everyone.
I know this is a rather straightforward topic, but I seem to be having trouble. If there is a reaction that is first order with respect to one reactant and second order with respect to another, then the shape of the concentration/time graph plotted from the concentration change of each reactant will differ, right? If I model the rate with a differential equation, the result equation of the concentration time graph for each reaction is obviously different.
If so, how can we measure the rate, the gradient at a point (say time t=a) from both graphs and get the same answer?? Won't the gradient be different?
Please enlighten me as to what I'm missing!

Thank you very much!!