SOLUTION: A tracker is expected to average at least 40 mph on his trip to werhouse,he drives to the werhouse at 20 mph .how fast must he drive back? thankyou

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: A tracker is expected to average at least 40 mph on his trip to werhouse,he drives to the werhouse at 20 mph .how fast must he drive back? thankyou      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


    

Question 323714: A tracker is expected to average at least 40 mph on his trip to werhouse,he drives to the werhouse at 20 mph .how fast must he drive back?
thankyou
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Since the distance to the warehouse is not given,
it can be any distance, and it doesn't change the problem
I'll say the distance is 40 mi
Let t = his time to drive back
Ave speed is (total distance)/(total time)
The total distance is 2%2A40+=+80 mi
The time driving to the warehouse is 40%2F20+=+2 hrs
Ave speed = 80%2F%282+%2B+t%29
40+=+80%2F%282+%2B+t%29
40%2A%282+%2B+t%29+=+80
2+%2B+t+=+2
t+=+0
My result is that he can't do it
If he was to average 39 mi/hr for the whole trip,
39%2A%282+%2B+t%29+=+80
2+%2B+t+=+2.0513
t+=+.0513 hr
Speed returning = 40%2F.0513+=+780 mi/hr
If he was to average 25 mi/hr
25%2A%282+%2B+t%29+=+80
2+%2B+t+=+3.2
t+=+1.2 hr
Speed returning = 40%2F1.2+=+33.33 mi/hr
So, an ave speed for the whole trip
needs to be around 25 or 30 mi/hr
Maybe there's a flaw in my logic,
but this is what I get