RRB ALP CBT I 17 Feb 2026 Shift 1 Paper

Concept:For a journey divided into three equal distances, average speed can be found by dividing total distance by total time, or by using the harmonic mean of the three speeds.Explanation:Each part of the journey is $160$ km, so total distance covered is:$160 + 160 + 160 = 480$ km.Time for the first part:$t_1 = \frac{160}{80} = 2$ hours.Time for the second part:$t_2 = \frac{160}{120} = \frac{4}{3}$ hours.Time for the third part:$t_3 = \frac{160}{80} = 2$ hours.Total time taken:$t = 2 + \frac{4}{3} + 2 = 4 + \frac{4}{3} = \frac{16}{3}$ hours.Now, average speed is:$\text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}} = \frac{480}{\frac{16}{3}} = 480 \times \frac{3}{16} = 90$ $\text{km/hr}$.Alternatively, since the distances are equal, use the harmonic mean:$\text{Average Speed} = \frac{3}{\frac{1}{80} + \frac{1}{120} + \frac{1}{80}} = \frac{3}{\frac{2}{80} + \frac{1}{120}} = \frac{3}{\frac{1}{40} + \frac{1}{120}} = \frac{3}{\frac{4}{120}} = 90$ $\text{km/hr}$.Answer:The average speed of the racer car for the entire journey is $90$ $\text{km/hr}$, which matches option C.