The average mass of 4 students in a team was 35 kg. When another student joined the team, the average mass of the 5 students became 33 kg. What was the mass of the student who just joined the team?

1. Calculate the total mass of the original 4 students

$\text{Total mass of 4 students} = 4 \times 35 = 140 \text{ kg}$

2. Calculate the total mass of the 5 students after the new student joins

$\text{Total mass of 5 students} = 5 \times 33 = 165 \text{ kg}$

3. Find the mass of the new student by taking the difference of the totals

$\text{Mass of new student} = 165 - 140 = 25 \text{ kg}$