Question 1143808
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The entire distance consists of three segments of the length  d = |AB|,  d = |BC|  and  2d = |CA|.


Hence, the average speed of the car at the entire journey is


    average speed = {{{(d + d + 2d)/(d/30 + d/40 + 2d/50)}}} = {{{4/(1/30 + 1/40 + 2/50)}}} = {{{4/(20/600 + 15/600 + 24/600)}}} = {{{(4*600)/(20 + 15 + 24)}}} = {{{(4*600)/59}}} = 40.678 kilometers per hour (approximately)
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