By increasing her usual speed by 20 kilometers per hour,

Question

a bus driver decreases the time on a 20-kilometer trip by 5 minutes. Find the usual speed.

Answer 1

d= r*t, where d=distance, r=speed, t=time,

 

Let her usual speed= x, and time= y 

20=x* y -------------------<1>

20=(x+20)(y-5/60) -------<2>

 

From <1>,  y=20/x -------<3>

<3>→<2>,  and simplify,  x² + 20x - 4800= 0 ------<4>

Factor <4> and solve for x, x= 60 k/h