a) 28 kmph
b) 27 kmph
c) 25 kmph
d) 24 kmph

Answer: c
Explanation: Let the speed of the train be S. And length of the train be x.
When a train crosses a man, its travels its own distance.
$$\eqalign{ & {\text{According to question}}; \cr & \frac{x}{{ {\left( {s – 3} \right) \times {\frac{5}{{18}}} } }} = 10 \cr & {\text{or}},\,18x = 50 \times s – 150…..({\text{i}}) \cr & {\text{and}} \cr & \frac{x}{{ {\left( {x – 5} \right) \times {\frac{5}{{18}}} } }} = 11 \cr & 18x = 55 \times s – 275……({\text{ii}}) \cr & {\text{Equating equation }}\left( {\text{i}} \right){\text{ and }}\left( {{\text{ii}}} \right) \cr & 50 \times s – 150 = 55 \times s – 275 \cr & {\text{or}},\,5 \times s = 125 \cr & {\text{or}},\,s = 25\,{\text{kmph}} \cr} $$