<PRE><B>Question 960356</B>
To travel from Singapore to Malacca, a distance of 280 km, a motorist finds that if he travels at an average speed of x km/h, he would have taken 20 minutes less than when he travels at an average speed of (x-8) km/h. Form an equation in x and find the time taken by the motorist if he travels at x km/h.
***
travel time=distance/speed
20 min=1/3 hr
{{{280/(x-8)-280/x=1/3}}}
lcd: x(x-8)
280x-280x+2240=(x^2-8x)/3
x^2-8x-6720=0
solve for x by quadratic formula:
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
a=1, b=-8, c=-6720
x=86.07
x-8=78.07
280/86.07=3.25
time taken by the motorist if he travels at x km/h=3.25 hrs</PRE>