Suppose there are 30 students who take a vacation during summer or winter. Of those, 18 take a vacation during summer and 4 take a vacation during summer and winter. How many take a vacation during winter?
Total students, N = 30
Summer = S
Winter = W
S or W = N
Students who take vacation in summer, S = 18
S + W only = 30
W only = 30 – S = 30 – 18 = 12
Students who take vacation in both summer and winter (intersection of S and W) = 4
Therefore to find the number of students who take vacation in winter we add the intersection number to the W only number.
Thus, W = 4 + 12 = 16