Question : A man goes to a place on the car at a speed of 144 km/hr and comes back at a lower speed. If the average speed is 60 km/hr in total, then find his returning speed.
Option 1: 40.05 km/hr
Option 2: 37.89 km/hr
Option 3: 33.33 km/hr
Option 4: 22.25 km/hr
Correct Answer: 37.89 km/hr
Solution :
Let the return speed of man be $x$.
Given,
Average speed = 60 km/hr
As we know, Average speed = $\frac{2xy}{x + y}$, where $x$ and $y$ are the speeds resp.
⇒ $60 = \frac{2 × 144 × x}{144 + x}$
⇒ $144+ x = \frac{288x}{60}$
⇒ $144 + x = 4.8x$
⇒ $3.8x = 144$
⇒ $x = \frac{144}{3.8}$
⇒ $x = 37.89$ km/hr
Hence, the correct answer is 37.89 km/hr.
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