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October 2nd, 2019, 11:23 PM  #1 
Senior Member Joined: Aug 2014 From: India Posts: 477 Thanks: 1  How to find average speed for this problem?
What is the average speed of a man who travels 1/4th distance at 10kmph, 1/3rd the distance at 20kmph and the rest at 12.5 kmph? Solution: Remaining time = 1 – (1/4 + 1/3) = 5/12 Multiplying 12 to fractions to get whole numbers; 3, 4 & 5. After this how to proceed? 
October 3rd, 2019, 02:52 AM  #2 
Senior Member Joined: Mar 2015 From: Universe 2.71828i3.14159 Posts: 132 Thanks: 49 Math Focus: Area of Circle 
Let the total distance be x. Travels (i) $1/4 \; distance \; at \; 10km/h \; t_0= \dfrac{x}{4} : 10 = \dfrac{x}{40}$ (ii) $1/3 \; distance \; at \; 20km/h \; t_1 = \dfrac{x}{60}$ (iii) $5/12 \; distance \; at \; 12.5km/h \; t_2 = \dfrac{x}{30}$ The total time it took $t_{total} = \dfrac{x}{40} + \dfrac{x}{60} + \dfrac{x}{30} = \dfrac{9x}{120} = \dfrac{3x}{40}$ Average velocity is the total distance divided by total time: $x: \dfrac{3x}{40}=\dfrac{40}{3}=13 \dfrac{1}{3}$ 

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