Question 630582
Christopher traveled by motorcycle at an average speed of 54 miles per hour. 
Then, he traveled by train at an average speed of 31 miles per hour. 
In total, he traveled 165 miles for 5 hours. 
How many miles did Christopher travel by train? (Round to the nearest mile.)
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let x=miles traveled by train
165-x=miles traveled by motorcycle
travel time=distance/speed
..
54/(165-x)+31/x=5
LCD:x(165-x)
54x+31(165-x)=5x(165-x)
54x+5115-31x=825x-5x^2
5x^2-802x+5115=0
solve by following quadratic formula:
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
a=5, b=-802, c-5115
ans:
x≈6.6538
miles traveled by train=7