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Message: <blockquote data-quote="MihiCherub" data-source="post: 15265666" data-attributes="member: 238676">correct... <img src="http://www.elakiri.com/forum/images/icons/sq/11.gif" alt="" class="fr-fic fr-dii fr-draggable " style="" />Average rate is not the average of the rates, the distance does not need to be known. Where a and b are the two rates, the average rate can be shown to be 2ab/(a + b), so 2(20)(60)/(20 + 60) = 30.Average rate = Total distance/Total time. Let’s say the distance is D one way. Then the total distance is 2D. Let’s say the time the car travels 20 mph is t and the time the car travels 60 mph is T. Then from the formula Rate × Time = Distance, 20 × t = D and 60 × T = D.This gives you t = D/20 and T = D/60. So the total time is,t + T = D/20 + D/60. This is equal to t + T = 80D/1,200 = D/15.So the average rate = 2D/(t + T) = 2D/(D/15) = 30.</blockquote>

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