Answer:
 12 students play chess 
and 25 students play Sudoku
Explanation:
There are 30 students in Ms Barclay's classroom.
2/5 students play chess. 
i.e. 
 play chess
i.e. 12 students play chess
5/6 of the students play Sudoku. 
i.e. 
 play Sudoku
i.e. 25 students play Sudoku
Hence, 12 students play chess 
and 25 students play Sudoku