A train travels 500 m in first minute. In the next 4 minutes, it travels in each minute 125 m more than that in the previous minute. The average speed per hour of the train during those 5 minutes will be

Distance travelled by the train in the first minute = 500m

In the second minute = 500+125 = 625m

In the third minute = 625+125 = 750m

Similarly in the 4th and 5th minutes distance travelled will be 875m and 1000m respectively.

Total distance travelled = 500+625+750+875+1000 = 3750m = 3.75 km

Total time taken = 5 min = $$\frac{1}{12}$$ hour

Average speed = $$\frac{3.75}{\frac{1}{12}}$$ = 3.75 * 12

= 45 kmph