Question 1081869
69C4 are the number of ways (864,501)
17C4 are all seniors, and probability is 0.0028m dividing 2380 by 864,501.
one of each is a numerator of 19C1*19C1*14C1*17C1=85918, probability is 0.0994.
2 sophomores and 2 freshmen are 19C2*19C2=29241 and probability is 0.0338
at least one is a senior is 1-no seniors, and no seniors has a numerator of 52C4.  That probability is 0.3132.
Therefore at least one senior is the complement or 0.6868.