Question 394139
Find the speed of the train if an increase of 6kph lowers the time for a journey of 72km by 10 minutes. (Show Your Solution)
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let speed =x mph
increase speed = x+12
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time = d/r
original time - increased speed time = 1/6 hours
{{{72/x-(72/(x+12))= 1/6}}}
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LCD = x(x+12)
{{{(72(x+12)-72x)/x(x+12)= 1/6
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{{{(72x+864-72x)/x(x+12)= 1/6}}}
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{{{864= (x(x+12))/6}}}
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6*864=x^2+12x
5184=x^2+12
x^2+12x-5184 =0
solve using quadratic formula
a=1, b= 12,c=-5184
b^2-4ac=20880
you will  get the speed = 66.24 kph
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m.ananth@hotmail.ca