In a Shimla school 20% of students play none of three games and 5% play all three. The note gives each game's percentage. What percentage play exactly one game?

At least one $=80\%$ = exactly one + exactly two + 5. The totals $40+35+30=105$ = exactly one + 2 × exactly two + $3\times 5$. Subtracting: exactly two $=105-80-10=15\%$, so exactly one $=80-15-5=60\%$. 75% is exactly one plus exactly two, 45% subtracts the 15 twice, and 65% forgets the 5% in the centre.