Question 94

A jet ski goes upstream at a speed of 48 km/hr and comes back the same distance at 80 km/hr. Find the average speed (in km/hr) for the total journey.

Solution

Let say, total distance is d km.

We know , Average speed = $$\frac{Total\ distance\ covered}{Total\ time\ taken\ in\ journey}.$$

So, Average speed = $$\frac{2d}{\frac{d}{48}+\frac{d}{80}}\ \frac{km}{h}=\frac{2d}{\frac{d\left(5+3\right)}{240}}\ \frac{km}{h}=60\ \frac{km}{h}.$$

D is correct choice.

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