In November 2018, the frequency tree shows us that 35 students aged 15 years old had part-time work.
That number 35 drops to 23 a year later in 2019. There are two reasons for this:
- The student lost their job. They got fired or quit their job.
- The 15 year old student had a birthday and turned 16.
Case (2) mentioned above only works if the student's birthday is before April 2019.