Amrutha drove from bangalore to chennai at 80km/hr and returned at 100km/hr.Find the average speed.

100km/hr

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98km/hr

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66.66km/hr

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88.88km/hr

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Solution

The correct option is D
88.88km/hr

Let the distance between Bangalore and Chennai be $x$ km.

From Banglaore to chennai,

$s p e e d = \frac{d i s t a n c e}{t i m e}$

$t = \frac{x}{80}$

From Chennai to Bangalore,

$t = \frac{x}{100}$

Total time taken $= \frac{x}{80} + \frac{x}{100}$

Taking LCM and adding, $\frac{5 x + 4 x}{400} = \frac{9 x}{400}$

Total distace travelled in the entire journey = $x + x = 2 x k m$

$A v e r a g e s p e e d = \frac{t o t a l d i s t a n c e}{t o t a l t i m e} = \frac{2 x}{\frac{9 x}{400}}$

$= \frac{2 \times 400}{9} = \frac{800}{9} = 88.8 k m / h r$

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