Lot of students gets confused while finding out the average speed, when various distances are travelled with different speed. Say for example, trip to Agra from Delhi is made at an average speed of 40 km/hr and the trip back at an average speed of 60 km/hr. Find their average speed for the entire trip. (Hint: It’s Not 50 Km/hr)
Rule: If a person travels a distance at a speed of x km/hr and the same distance at a speed of y km/hr, then the average speed during the whole journey is given by 2xy/x + y km/hr.
Or, If a person travels half the distance at a speed of x km/hr and the other half at a speed of y km/hr, then the average speed during the whole journey is given by 2xy/x + y km/hr.
So answer to the above question:
(2*60*40)/(60+40) = 48 Km/hr
If a person travels three equal distances at a speed of x km/hr, y km/hr and z km/hr respectively, then the average speed during the whole journey is 3xyz/xy + yz + xz km/hr.
This problem can also be dealt with assuming some hypothetical distance.
You can find thousands of such amazing faster calculation tricks in the “MAGICAL BOOK on QUICKER MATHS – by M. Tyra“
If you’ve a question related to time and speed or any other topic in maths, you can post it on QuickerMaths.com’s question answer platform