SOLUTION: a bus leaves chicago every friday at 5:oopm for a 264 mi trip to another city.this week the bus leaves at 5:30 pm.To arrive in the same city on time,the driver drives 4 miles per

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Question 722099: a bus leaves chicago every friday at 5:oopm for a 264 mi trip to another city.this week the bus leaves at 5:30 pm.To arrive in the same city on time,the driver drives 4 miles per hour faster than usual.what is the usual bus's speed
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
let the speed of bus be x
time taken to reach the city = 264/x
speed increased by 4
speed = x+4
Time taken to reach city now = 264/(x+4)
After increase in speed it takes 1/2 hour less
It reaches same time
264/x - 264/(x+4) = 1/2
multiply by 2x(x+4)
264*2(x+4)-2*264x=x(x+4)
528x+2112-528x=x^2+4x
x^2+4x-2112=0
x^2+4x+4 = 2112+4
(x+2)^2= 2116
take square root
x+2 = +/- 46
x= 44 OR -48
ignore negative