Let sum of marks of students be $x$ Now therefore $x = 25×50 =1250$ Now to maximize the marks of the toppers We will minimize the marks of $20 \students$ so their scores will be $(30,31,32.....49 )$ let score of toppers be $y$ So we get $5\y + 20/2 (79)=1250 $ we get $5y +790=1250$ $5\y=460 $ $ \y=92$ So scores of toppers $= 92$