How much percentage should a racer increase speed to reduce the time by 20% to cover a fixed distance?

25%

Time is reduced by 20%

Ratio of old to new speed  = 5 : 4

Distance = Speed × Time

Speed is inversely proportional to time

So , Ratio of Speed is  4 : 5

Old and New distance both are same .

So , Percentage increase in speed = \(\frac{1}{4}\) × 100 = 25%