SOLUTION: The averages speed of an automobile for the first half of a 100 km. trip was
60 km/hr and from the second half was 90 km/hr. What was the average speed in
km/hr for the entire
Algebra ->
Customizable Word Problem Solvers
-> Travel
-> SOLUTION: The averages speed of an automobile for the first half of a 100 km. trip was
60 km/hr and from the second half was 90 km/hr. What was the average speed in
km/hr for the entire
Log On
Question 272215: The averages speed of an automobile for the first half of a 100 km. trip was
60 km/hr and from the second half was 90 km/hr. What was the average speed in
km/hr for the entire distance?
(A) 68 (B) 72 (C) 75 D) 78 (E) 80
You can put this solution on YOUR website! Distance(d) equals Rate(r) times Time(t) or d=r/t; r=d/t and t=d/r
Average Speed=(Total Distance)/(Total Time)
Total Distance = 100km
Total Time=Time for the 1st half + Time for the 2nd half
Time for the 1st half=50/60=5/6 hr
Time for the 2nd half=50/90=5/9 hr
So,
Average Speed=100/(5/6+5/9)
Average Speed=100/(15/18 +10/18)
Average Speed=100/(25/18) multiply numerator and denominator by 18/25
Average Speed=100(18/25)/1=4*18=72 km/hr
