Answer:
there are 97 + 47 + 77 = 221 creatures from Earth in the alien spaceship.
the probability that a human being is chosen at random = 77 / 221 = 0.3484 = 34.84%
the probability that a chicken is chosen at random = 97 / 221 = 0.4389 = 43.89%
the probability of choosing a cow at random = 100% - 34.84% - 43.89% = 21.27%