# Homework Help: Avg speed help

1. Aug 27, 2007

### camboguy

ok heres 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???

2. Aug 27, 2007

### 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

3. Aug 27, 2007

### camboguy

aaaa i see thank you

4. Aug 27, 2007

### 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