The number of years in which there was an increase in revenue from at least…

Concept

To test whether a category increased in a year, compare its revenue with the immediately preceding year. Count a year only when at least two categories have strictly larger values than in that preceding year.

The first listed year provides the baseline; only later years can be assessed for an increase.

Application

1. For 2013 versus 2012: journals rise from 46 to 47, magazines from 31 to 39, and books from 73 to 77. All three categories increase, so 2013 is counted.

2. For 2014 versus 2013: journals fall from 47 to 45, magazines rise from 39 to 46, and books rise from 77 to 78. Two categories increase, so 2014 is counted.

3. For 2015 versus 2014: journals fall from 45 to 44, magazines rise from 46 to 51, and books remain 78. Only one category increases, so 2015 is not counted.

Cross-check

The numbers of increasing categories in the three comparable years are 3, 2, and 1. Exactly the first two meet the threshold of at least two categories.

Therefore, the required number of years is 2.