Calculating Avg Speed of Round Trip: What's Wrong?

[camboguy]

ok here's the question then what i did so far.

Q> calculate the avg speed of a complete round trip in which the first 200km is covered at 90km/hr, followed by a one-hour lunch break, and final 200km is covered at 50km/hr.


What i tried> 200km/90kmphr then i got 2.2hr and then 200/2.2hr to get the avg speed, which was 90km.

then i did 200km/50kmphr then i got 4hr and then 200km/4hr and got 50km. then avg those speeds but i keep geting around 70 and the answer is supposed to be 55km/hr.

what am i doing wrong?

 

[rootX]

"and then 200/2.2hr to get the avg speed, which was 90km."

but you are missing first half with the second half?

average speed = total distance travelled/total time

so total dist = 400
and total time =2.2+4+1

 

[camboguy]

aaaa i see thank you

 

[rootX]

ohh.. now I got it, what you were doing there.. "200/2.2"
I think it would have worked if they hadn't stopped for the break