By increasing her usual speed by 20 kilometers per hour, a bus driver decreases the time on a 20-kilometer trip by 10 minutes. Find the usual speed.

Answer 1

time = distance/speed

t = d/s

20/(x+20 =t- 1/6 hr=t- 10 minutes

20/(x+20)= (6t-1)/6

x+20)(6t-1) =6(20)= 120

d=xt=20

t=20/x

(x+20)(120/x -1) = 120

120 -20 -x + 2400/x = 120

-x^2 -20x +2400 = 0

(x+60)(x-40)=0

x=40 kph= regular bus speed

regular time = 20/40 = 1/2 hour = 30 minutes

shorter time = 20/60 = 1/3 hour = 20 minutes = 10 minutes faster

x