SOLUTION: 1/4 journey at 25 km/h 1/3 at 30km/h and rest at 50km/h.find average speed

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: 1/4 journey at 25 km/h 1/3 at 30km/h and rest at 50km/h.find average speed      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


    

Question 997465: 1/4 journey at 25 km/h 1/3 at 30km/h and rest at 50km/h.find average speed
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
1/4 journey at 25 km/h 1/3 at 30km/h and rest at 50km/h.
find average speed
:
Let a = the average speed
We can make this easy, choose a convenient value for the distance of the trip
Dist = 120 km
them
1%2F4*120 = 30 km
1%2F3*120 = 40 km
and
50 km = the remainder of the trip
:
Write a time equation; time = dist/speed
30%2F25 + 40%2F30 + 50%2F50 = 120%2Fa
Multiply equation by 150a, cancel the denominators and you have
6a(30) + 5a(40) + 3a(50) = 150(120)
180a + 200a + 150a = 18000
530a = 18000
a = 18000/530
a = 33.96 ~ 34 km/hr is the average speed