A traffic signal has three colors: green, yellow, and red, which appear with the

following probabilities. Using a unigram model, what is the perplexity of the

sequence $($green$,$ yellow, red$)?$

$P($ green $)=\frac{3}{5},P($ yellow $)=\frac{1}{5},P($ red $)=\frac{1}{5}$