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4.Average
medium
The average speed of a cyclist who covers first, second and third km at $20,16$ and $12\, km / hr$ respectively ( in $km / hr )$ is
A
$16.24$
B
$16$
C
$15.66$
D
$15.32$
Solution
Let the average speed of a cyclist $= x$
Total distance $=3 \,km$
$\frac{1}{20}+\frac{1}{16}+\frac{1}{12}=\frac{3}{x} \Rightarrow \frac{12+15+20}{240}=\frac{3}{x}$
$\frac{47}{240}=\frac{3}{x} x=15.32 \,km / hr$
Average speed of cyclist is $15.32\, km / hr$
Standard 13
Quantitative Aptitude