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Mr. Bundda travels in his car and covers 1/4 part of his journey with 8 km/h, 3/5 part with 6 km/h and remaining 3/20 part with a speed of 10 km/h. Find out his average speed during the whole journey.


A) 6.83 km/h

B) 9 km/h

C) 4 km/h

D) 8.5 km/h

Correct Answer:
A) 6.83 km/h

Description for Correct answer:
According to the average speed formula

\( \Large P=\frac{1}{4},\ Q=\frac{3}{5},\ R=\frac{3}{20} \)

x = 8 km/h, y = 6 km/h, z = 10 km/h

Required average speed = \( \Large \frac{1}{\frac{P}{x}+\frac{Q}{y}+\frac{R}{z}} \)

=\( \Large \frac{1}{\frac{1}{4 \times 8}+\frac{3}{5 \times 6}+\frac{3}{20 \times 10}} \)

=\( \Large \frac{1}{\frac{1}{32}+\frac{1}{10}+\frac{3}{200}} \)

=\( \Large \frac{1}{\frac{25+80+12}{800}}=\frac{800}{117} \) = 6.83 km/h

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