Question 28741
MAry's speed = x
Rob's = x+8
Total milies driven by them both = 550.
time taken = one hour less = -1 so x+8-x=1


Equation:
{{{550/(x+8)-550/x=1}}}
550[(x+8)-(x)]=(x)(x+8)
{{{550(8)=x^2+8x}}}
{{{4400=x^2+8x}}}
{{{x^2+8x-4400=0}}}
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}} 
{{{x=(-8+-sqrt((8^2)-4*1*-4400))/(2*1)}}}
simplfy get two solutions.
Delete the negative answer.
{{{x=4(2sqrt(69-1))}}}
x=58 (rounded)
58+8=66


Hence, Mary's speed is 58mph and Rob's speed is 66 mph.
Paul.