Average speed of a cyclist who covers first, second and third km at 20,16 and 12, km / hr respective

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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

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