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A small aeroplane can travel at 320 km/hr in still air. The wind is blowing at a constant speed of 40 km/hr. The total time for a journey against the wind is 135 minutes. What will be the time, in minutes for the return journey with the wind? (Ignore take off and landing times for the aeroplane.) (a) 94.5 (b) 105 (c) 108.125 (d) 120 |
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Answer» (b) 105 min Speed of the aeroplane in still air = 320 km/hr Speed of wind = 40 km/hr ∴ Aeroplane will travel with the wind at (320 + 40) = 360 km/hr and Aeroplane will travel against the wind at (320 – 40) = 280 km/hr Suppose the distance to be travelled = x km Then, \(\frac{x}{280}=\frac{135}{60}\) hrs = \(\frac94\) hrs ⇒ x = \(\frac{280\times9}{4}\) = 630 km ∴ Time taken to cover a distance of 630 km at 360 km/hr is = \(\bigg(\frac{630}{360}\times60\bigg)\) min= 105 min. |
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