Question 57

Going downstream a boat covers 50 miles at a speed of 60 mph. While returning it takes 1 hour 15 minutes to cover the same distance. What is the average speed for the whole journey?

Solution

Average speed when speeds for same distance

$$ avg speed = \frac{2 \times x \times y}{x+y} $$

Downstream distance covered= 50 miles

upstream distance covered=50 miles

downstream speed = 60 mph

$$ upstream speed = 50 \times \frac{4}{5} $$

= 40 mph

$$ avg speed = \frac{2 \times 60 \times 40}{60+40} $$

= 48 mph

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