<PRE><B>Question 1057615</B>
Using rate * time = distance, we have two formulas
:
1) t1 = 1/30
2) t2 = 1/60
:
total time t = 1 * ( 1/30 + 1/60 )
:
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average speed = (2 * 1) / ( 1 * ( 1/30 + 1/60 ) ) = 2 / ( 1/30 + 1/60 ) = 40 mph
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