Question 662142
  <pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
speed x to town, 240km from home 
if his speed is increased by 10km/h{{{highlight(x+10)}}} then he will take 48 minutes(.8hr) less
 t = D/r
 {{{240/x - 8/10 = 240/(x+10)}}} |Multiplying thru by 10x(x+10) so as all denominators = 1
 2400(x+10) - 8x(x+10) = 2400x
 2400x + 24000 - 8x^2 - 80x = 2400x
    -8x^2 - 80x + 24000 = 0
     x^2 + 10x - 3000 = 0
factoring
   (x + 60)(x-50)= 0,   x = 50mph   (throwing out negative solution for unit measure)
and ...
 {{{240/50 - .8hr = 240/60 = 4hr}}}