In a race of 600 m, A can beat B by 30 m and in a race of 500 m, B can beat C by 25 m. By how many metres will A beat C in a race of of 400 m?

If A runs 600 m, then B runs 570 m.
If A runs 400 m, B then runs (570/600) x 400 m = 380 m
When B runs 500 m, then C runs 475 m,
When B runs 380 m, then C runs (475/500) x 380 = 361 m
∴ A beats C by (400 - 361) = 39 m