Question 683843
A man drove 156 km at a constant rate. If he had driven 5km/hr. faster he would made the trip in 12 minutes less time. How fast did he drive? 
ans. 60 KPH 
**
let x=how fast he drove
x+5=speed in 12 min less time
156/x-156/(x+5)=12 min=12/60 hr=0.2 hr
156/x-156/(x+5)=.2
LCD: x(x+5)
156(x+5)+156x=x(x+5)(.2)
156x+780+156x=.2x^2+x
.2x^2+x-780=0
2x+10x-7800=0
x+5x-3900=0
(x+65)(x-60)=0
x+65=0
x=-65(reject, x>0)
or
x-60=0
x=60
how fast he drove=60 km/hr