It takes mary x hours to travel 100 kilometers. If she increases her speed by 5 kilometers per hour, the journey will take her 3 hours less time. Find x.
her original speed be v
then vx = 100
her faster speed = v+5
(x-3)(v+5) = 100
xv + 5x - 3v - 15 = 100
100 + 5x - 3v = 115
5x - 3v = 15
v = (5x-15)/3
sub into 1st
x((5x-15)/3) = 100
5x^2 -15x = 300
x^2 - 3x - 60 = 0
I get x = 9.39 by using the formula (and v = 10.65)
check: (9.39)(10.65) = 100.0035
(6.39)(15.65) = 100.0035
YEAHH!