SOLUTION: a bakery delivery truck leaves the bakery at 5:00am each morning on its 144 mile route.one day the driver gets a late start and does not leve the bakery until 5:20am. to finish her

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Question 721995: a bakery delivery truck leaves the bakery at 5:00am each morning on its 144 mile route.one day the driver gets a late start and does not leve the bakery until 5:20am. to finish her route on time the driver drives 4 miles per hour faster than usual.at what speed does she usually drive ?
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
usual speed be x
today's speed = x+4
difference in time = 1/3 hours ( 20 min)
Usual time - today's time = 1/3
144%2Fx+-+144%2F%28x%2B4%29+=+1%2F3

multiply equation by 3x(x+4)

144%2A3%28x%2B4%29-144%2A3%2Ax=+x%28x%2B4%29

432x+1728-432x=x^2+4x
x^2+4x-1728=0
solve this you will get the usual speed which is 39.62