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Last updated at June 6, 2019 by Teachoo

Transcript

NCERT Question 3 Abdul, while driving to school, computes the average speed for his trip to be 20 km hโ1. On his return trip along the same route, there is less traffic and the average speed is 30 km hโ1. What is the average speed for Abdulโs trip? We know that Average speed = (๐๐๐ก๐๐ ๐๐๐ ๐ก๐๐๐๐)/(๐๐๐ก๐๐ ๐ก๐๐๐) Let Distance between Abdulโs Home and School be d Now, Since he goes from home to school, and then back Total Distance = d + d = 2d To find Total Time, we find Time taken to go from Home to School, and from School to Home Let time taken to reach home = ๐ก_2 Home to School Distance = d Speed = 20 km/h Speed = ๐ท๐๐ ๐ก๐๐๐๐/๐๐๐๐ 20 = ๐/๐๐๐๐ โด Time = ๐/20 School to Home Distance = d Speed = 30 km/h Speed = ๐ท๐๐ ๐ก๐๐๐๐/๐๐๐๐ 30 = ๐/๐๐๐๐ โด Time = ๐/30 Total time taken = ๐/20 + ๐/30 = (3๐ + 2๐)/60 = 5๐/60 = ๐/12 Average speed = (๐๐๐ก๐๐ ๐๐๐ ๐๐ก๐๐๐)/(๐๐๐ก๐๐ ๐ก๐๐๐) = 2๐/(๐/12) = (2๐ ร 12)/๐ = 24 km/h

Class 9

Chapter 8 Class 9 - Motion

About the Author

CA Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo