SOLUTION: A Motorist travels 90 kms. with the speed of 60 km/hr and the next 40 kms distance with the speed of 40 km/hr. what is his average speed during the journey?
1) 50kms/hr
2) 100k
Algebra.Com
Question 861765: A Motorist travels 90 kms. with the speed of 60 km/hr and the next 40 kms distance with the speed of 40 km/hr. what is his average speed during the journey?
1) 50kms/hr
2) 100kms/hr
3) 45kms/hr
4) 48kms/hr
My Solution:
Finding times for two cases by the formula Total Time = Total Distance / Avg. Speed
Case 1:
Time = 90kms / 60kms/hr = 1.5hrs
Case 2:
Time = 40kms / 40kms/hr = 1hr
Adding two times = 2.5hrs
Adding two distances = 130kms
We find avg speed = 130 / 2.5 = 52kms/hr
But the answer is wrong this way.
One more simple thing i did is find the average of = (40 kms/hr + 60 kms/hr)/2 = 50km/hr which is also wrong.
The Answer is 48km/hr. Please explain how.
Found 2 solutions by richwmiller, ankor@dixie-net.com:
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
The answer is 52.
r*t=d
r=d/t
To get average speed you take total distance /total time=average speed
90/60=1.5 hours
40/40=1
1+1.5=2.5 hours
90+40=130
130/2.5=52
the book is wrong.
They must have changed the problem and forgot to change the solution and choices.
Unfortunately that happens all too often.
Double check the numbers and make sure you copied them correctly.
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
A Motorist travels 90 kms. with the speed of 60 km/hr and the next 40 kms distance with the speed of 40 km/hr.
what is his average speed during the journey?
:
let a = his average speed for the journey
:
The total distance is 90 + 40 = 130 km
Write a time equation; Time = dist/speed
+ =
1.5 + 1 =
2.5a = 130
a = 52 km/hr is the av speed so are right|
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