Probability question

Hi All
Need your help to solve below question of probability.
Question: There are 300 students in an online MBA program for working professionals, for whom the attendance in online classes is 70%, i.e. on an average, 210 students are present in an online session. Fifty new students are admitted in this batch.
a) What is the probability of attendance being at least 70% among the new students, thus ensuring the overall attendance does not fall below 70%?
b) The Program Dean thinks that this probability will increase, if the new batch size is 40 instead of 50 students. Is he right in assuming so?


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Are we to make the assumption that the true probability that each of the 50 new students will attend or not ends up being 70%?