Question 376163
let speed for 330 miles be x
next 30 miles x-25 mph.
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time for 330 miles +time for 30 miles = 7
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t=d/r
330/x + 30/(x-25)=7
LCD = x(x-25)
(330(x-25)+30x )/(x(x-25)= 7
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(330x-8250+30x)/(x(x-25)=7
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360x-8250 = 7*(x(x-25)
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360x-8250 = 7x^2-175x
7x^2-360x-175x+8250=0
7x^2-535x+8250=0
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find roots x1,x2 by quadratic formula
discriminant =b^2-4ac= 55225
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x1=(535+sqrt(55225))/14
x1=55 mph
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x2= (535-sqrt(55225))/14
x2=21.42 mph. ( not possible since speed was reduced by 25 mph.)
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So speed = 55 mph for the 330 mile part
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m.ananth@hotmail.ca