A can finish 2400m race in 1 minute 50 sec. While B can finish the same race in 2 minutes . By what distance A will defeat B in a race of 2400 m.

200m

According to question , 

A runs a distance of 2400m in 1 minutes 50sec and B runs same distance in 2 minutes  . 

A  beats B by 10 sec 

Distance travelled by B in  2 minutes  ( = 120 sec ) = 2400m 

Distance travelled by B in 10 sec = \(\frac{2400\;×\;10}{120}\) = 200m