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4.Average
medium
A person travelled from one place to another at an average speed of $40 \,km / h$ and back to the original place at an average speed of $50\, km / h$. What is his average speed in $km / h$ during the entire trip?
A
$45$
B
$20 \sqrt{5}$
C
$400 / 9$
D
$50$
Solution
Average speed of the person for his whole journey $=\frac{2 \times 40 \times 50}{(40+50)}=\frac{4000}{90}=\frac{400}{9} km / hr$
Std 13
Quantitative Aptitude