SOLUTION: A man jogged 3.5 km/h in 20 min. He then walked the remainder of the 5.5 km at an average speed of 5 km/h. Given that he did not stop to rest during the entire distance of 5.5 km,

Algebra ->  Percentage-and-ratio-word-problems -> SOLUTION: A man jogged 3.5 km/h in 20 min. He then walked the remainder of the 5.5 km at an average speed of 5 km/h. Given that he did not stop to rest during the entire distance of 5.5 km,       Log On


   

Question 1020035: A man jogged 3.5 km/h in 20 min. He then walked the remainder of the 5.5 km at an average speed of 5 km/h. Given that he did not stop to rest during the entire distance of 5.5 km, calculate his average speed in km/h for the Whole journey.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A man jogged 3.5 km/h in 20 min.
He then walked the remainder of the 5.5 km at an average speed of 5 km/h.
Given that he did not stop to rest during the entire distance of 5.5 km, calculate his average speed in km/h for the Whole journey.
:
Let a = his average speed of the journey
:
Change 20 min to 1/3 hrs
:
Write a time equation; time = dist/speed
1st 3.5 km time + remaining 2km time = total time
1%2F3 + 2%2F5 = 5.5%2Fa
multiply by 15a
15a*1%2F3 + 15a*2%2F5 = 15a5.5%2Fa
Cancel the denominators and you have
5a + 3a(2) = 15(5.5)
5a + 6a = 82.5
11a = 82.5
a = 82.5/11
a = 7.5 km/hr is the average speed of the whole trip