After 40 minutes into a race, Michael has run ⁸₁₁ of the route while Riordan has covered only ²₁₁ of the distance. Michael runs at the same average speed throughout the race and Riordan’s average speed is 120 m/min slower than Michael’s. If Riordan wants to finish the race at the same time as Michael, by how many percent should he increase his average speed by for the remaining part of the race? Round off your answer to the nearest whole number.
Extra distance that Michael ran more than Riordan in first 40 min
= 40 x 120
= 4800 m

Fraction of the entire distance that was covered by Michael more than Riordan in the first 40 min
= ⁸₁₁ - ²₁₁
= ⁶₁₁

⁶₁₁ of the entire distance = 4800 m
¹₁₁ of the entire distance = 4800 ÷ 6 = 800 m

Distance that Riordan ran in the first 40 min
= 2 x 800
= 1600 m

Riordan's average speed
= 1600 ÷ 40
= 40 m/min

Michael's average speed
= 40 + 120
= 160 m/min

Fraction of the journey that Michael needed to run to complete the race
= 1 - ⁸₁₁
= ³₁₁

¹₁₁ of the entire distance = 800 m
³₁₁ of the entire distance = 3 x 800 = 2400 m

Duration that Michael would take to complete
= 2400 ÷ 160
= 15 min

Fraction of the journey that Michael needed to run to complete the race
= 1 - ²₁₁
= ⁹₁₁

⁹₁₁ of the entire distance = 9 x 800 = 7200 m  

Speed that Riordan needs to take to complete distance at the same time as Michael
= 7200 ÷ 15
= 480 m/min

Increase in Riordan's average speed
= 480 - 40
= 440 m/min

Percentage increase in Riordan's average speed
= ⁴⁴⁰₄₀ x 100%
≈ 1100%

Answer(s): 1100%