Question 380432
Distance = 800 miles . speed going = x mph
distance = 800 miles : speed = x+40 mph.
...
time going +time returning=8
..
t=d/r
800/x+800/(x+40 )= 8
..
lcd = x(x+40)
800(x+40)+800x /x(x+40)=8
800x+32000+800x=8x^2+320x
8x^2-1600x+320x-32000=0
8x^2-1280x-32000=0
/8
x^2-160x-4000=0
..
find the roots x1,x2 using quadratic formula
discriminant = 41600
x1=((160+sqrt(41600))/2
x1= 181.98 = 182 mph 
x2 is negative so reject.
return trip speed = x+40 = 182 +40 = 222 mph
...
m.ananth@hotmail.ca