<PRE><B>Question 914830</B>
Aeroplane left 30 minutes later than its scheduled time and in order to reach distination 1500 KM away in time,it has to increase its speed by 250 km/h from its usual speed.determine it usual speed
***
let x=usual speed of plane
x+250=increased speed of plane
30 min=1/2 hr
travel time=distance/speed
...
{{{1500/x-1500/(x+250)=1/2}}}
lcd:x(x+250)
1500(x+250)-1500x=x(x+250)/2
1500x+375000-1500x=x^2+250x/2
750000=x^2+250x
x^2+250x-750000=0
(x+1000)(x-750)=0
x=750
usual speed of plane=750 km/hr</PRE>