2022 · Q107
A car travels 3/4th of the distance at a speed of 60 km/hr and the remaining 1/4th of the distance at a speed of V km/hr. If the average speed for the full journey is 50 km/hr then the value of v is
general-mental-abilityquantitative-aptitude
- A40
- B30
- C100/3
- D35
Explanation
Let the distance be D km. Time for the first 3D/4 at 60 km/h is D/80 h, and for the last D/4 at v km/h is D/(4v) h. Average speed = D/(D/80 + D/4v) = 50, giving 1/80 + 1/(4v) = 1/50, so 1/(4v) = 3/400 and v = 100/3 km/h. Note this is below 50, as expected for a harmonic-mean average weighted toward the slower leg.