A can beat B by 5 meters in 100 m and B can beat C by 15 meters in 200 m race. A can beat C in 400 m race by:

∴ A runs 100 m while B runs 95 m
∴ A runs 400 m while B runs 95 x 400 / 100 = 380 m
Again, B runs 200 m while C runs 185 m
∴ B runs 380 m while C runs 185 x 200 / 380 = 3515 / 10 = 351.5 m
Hence, A runs 400 m while C runs 351.5 m
So, A can beat C by (400 – 351.5) = 48.5 m