The number of consumers in the age group 18-25 who prefer only one drink is

Let's tabulate all the information from the given table:

The calculation is as follows:

Consider the male 18 - 25 range:

=> Total consumers = 600

=> Out of them, 240 like A, 180 like B, 90 like both

=> Number of people who like either = 240 + 180 - 90 = 330

=> 600 - 330 = 270 people don't like any of the drinks.

Doing the same calculation for all the categories and tabulating, we get:

In 18-25:

Males: Number of people who only prefer 1 drink = 240 + 180 - 2*90 [subtracting those who like both] = 240

Females: 180 + 120 - 2*60 = 180

=> Required answer = 240 + 180 = 420.