There are 3 runners named A,B and C on the track. During a Race between them, when A reaches the finish line B is 20 meters behind A and C is 20 meters behind B. and when B reaches finish line C is 21 meters behind B. What is the length of Race track ?

When A finishes the track of length L, B is at L-20 and C is at L-40. The speed ratios are vB/vA = (L-20)/L and vC/vA = (L-40)/L, giving vC/vB = (L-40)/(L-20). When B finishes (travels the remaining 20m), C travels 19m (since C is 21m behind instead of 20m). Therefore (L-40)/(L-20) = 19/20. Cross-multiplying: 20L - 800 = 19L - 380, giving L = 420 meters.