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 A plane left 30 minutes late than its scheduled time and in order to reach the destination 1500 km away in time, it had to increase its speed by 100 km/h from the usual speed. Find its usual speed. 

 

Answers (1)

Let the usual speed of plane be x Km /hr 

Time taken to cover 1500 km with usual speed = \frac{1500}{x} hrs

Time taken to cover 1500 km with usual speed (x+100)

 =   \frac{1500}{x+100} hrs

\frac{1500}{x}= \frac{1500}{x+100} +\frac{1}{2}

\frac{1500}{x}- \frac{1500}{x+100} = \frac{1}{2}\\\\ x^2 +100 x -300000\\\\ (x+600 ) (x-500) = 0 \\\\ x \neq -600 \\\\ so, x = 500

speed of plane = 500 Km\hr

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Safeer PP

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