Answer
See below.
Work Step by Step
In this case the probability of guessing correctly will be $\frac{1}{3}$ and of guessing incorrectly will be $\frac{2}{3}$.
By definition, the expected value is the sum of each outcome multiplied by its probability. Hence here the expected value: $\frac{1}{3}\cdot1+\frac{2}{3}\cdot(-\frac{1}{4})=\frac{1}{6}$, which is positive, thus it is worth guessing.
