# Can anyone help with an average speed problem?

1. Sep 25, 2011

### wtp08

1. The problem statement, all variables and given/known data

A racing team of 3 drivers drove a 24 hour event in shifts. The first driver drove only one fourth of the race but averaged 140km/hr. The second driver drove one third of the race at an average speed of 170 km/hr. The last driver drove the remainder of the race at 160 km/hr. What was the average speed of the team?

2. Relevant equations
I do not know how to set up the problem in order to find average speed since there is no specific distance

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Sep 25, 2011

### Millacol88

Well, this is kind of an odd question. I would think that a weighted average could work. E.g. multiply the first speed by 1/4, the second by 1/3, and the third by 5/12. Then add these numbers together. See if that gives you the right answer, I'm not entirely sure.

3. Sep 25, 2011

### Uthobin

You have the total time: T=24h
Then, t1=$\frac{1}{4}$T=6h
t2=$\frac{1}{3}$T=8h
t3=$\frac{5}{12}$T=10h

The distance of each shift:
d1=v1*t1
d2=v2*t2
d3=v3*t3

Now you have the total distance and the total time, so you can calculate the average speed.

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