The total number of sample space in this item is calculated by adding up all the number of students given. That is,
S = 600 + 400 + 300 + 200 = 1500
The probability is calculated with the equation below.
P = n / S
where P is the probability,
n is the number of sophomores, and
S is the total number of students
Substituting,
P = 400 / 1500 = 4/15
ANSWER: 4/15