After 35 minutes into a race, Zeph has run ⁵₁₁ of the route while Luke has covered only ³₁₁ of the distance. Zeph runs at the same average speed throughout the race and Luke’s average speed is 120 m/min slower than Zeph’s. If Luke wants to finish the race at the same time as Zeph, 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 Zeph ran more than Luke in first 35 min
= 35 x 120
= 4200 m

Fraction of the entire distance that was covered by Zeph more than Luke in the first 35 min
= ⁵₁₁ - ³₁₁
= ²₁₁

²₁₁ of the entire distance = 4200 m
¹₁₁ of the entire distance = 4200 ÷ 2 = 2100 m

Distance that Luke ran in the first 35 min
= 3 x 2100
= 6300 m

Luke's average speed
= 6300 ÷ 35
= 180 m/min

Zeph's average speed
= 180 + 120
= 300 m/min

Fraction of the journey that Zeph needed to run to complete the race
= 1 - ⁵₁₁
= ⁶₁₁

¹₁₁ of the entire distance = 2100 m
⁶₁₁ of the entire distance = 6 x 2100 = 12600 m

Duration that Zeph would take to complete
= 12600 ÷ 300
= 42 min

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

⁸₁₁ of the entire distance = 8 x 2100 = 16800 m  

Speed that Luke needs to take to complete distance at the same time as Zeph
= 16800 ÷ 42
= 400 m/min

Increase in Luke's average speed
= 400 - 180
= 220 m/min

Percentage increase in Luke's average speed
= ²²⁰₁₈₀ x 100%
≈ 122%

Answer(s): 122%