Question #69c90

You can see that two resistors have been placed on the very right-hand branch. The $1 \Omega$ and the $3 \Omega$ resistor are connected in series. That means the total resistance of this branch needs to be found using ${R}_{T} = {R}_{1} + {R}_{2}$, giving a total resistance on this branch of $4 \Omega$.
If, instead, these two resistors were placed in two different parallel branches, by using $\frac{1}{R} _ T = \frac{1}{R} _ 1 + \frac{1}{R} _ 2$, the total resistance of those two resistors would be only $0.75 \Omega$.