SOLUTION: A car travels half of the distance with speed of 54km/h. what would be the speed for second half to get the average speed of 90km /h for whole journey.

Question 1093051: A car travels half of the distance with speed of 54km/h. what would be the speed for second half to get the average speed of 90km /h for whole journey.
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
A car travels half of the distance with speed of 54km/h. what would be the speed for second half to get the average speed of 90km /h for whole journey.
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d = 1/2 the distance
r = speed of 2nd half
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d/54 + d/r = 2d/90 = d/45
1/54 + 1/r = 1/45
(r+54)/54r = 1/45
r+54 = 54r/45 = 6r/5
5r + 270 = 6r
r = 270 km/hr
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Check:
Avg speed = 2*54*270/(54+270) = 90

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