- 56 km/hr
- 63 km/hr
- 120 km/hr
- 126 km/hr

Option 4 : 126 km/hr

Let's discuss the concepts related to Speed Time and Distance and Partial Speed. Explore more from Quantitative Aptitude here. Learn now!

Let usual speed of car be ‘x’ km/hr,

A car left 3 minutes early than the scheduled time and in order to reach the destination 126 km away in time, it has to slow its speed by 6 km/hr from the usual,

⇒ 126/ (x – 6) – 126/x = 3/60

⇒ 126 × [1/ (x – 6) – 1/x] = 3/60

⇒ x^{2 }– 6x – 126 × 120 = 0

⇒ x^{2 }– 126x + 120x – 126 × 120 = 0

⇒ x (x – 126) + 120(x – 120) = 0

⇒ x = 126

∴ Usual speed of car, x = 126 km/hr
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