No, you should not use the same approach from part (a) to
calculate the expected number of smokers among these 27 students because these
twenty seven students are not a random sample from the university’s total
population, example it might be argued that the proportion of smokers among the
27 students outside the gym at 9 am on Saturday morning would be lower than the
proper population of the university as a whole.
To add, a subset of a statistical population in wherein
each member of the subset has an equal probability of being chosen is
called a simple random sample.