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

So ,

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

Summer = S

Winter = W

S or W = N

Students who take vacation in summer, S = 18

S + W only = 30

So ,

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