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lopezsback · Jul 7, 2011, 06:01 PM

What is formula in solving average speed?

ballengerb1 · Jul 7, 2011, 06:04 PM

Add all of the speeds and divide by the number of samples. I.E. 100 mph, 200 mph and 225 mph add up to 425 mph divide by 3 results in 175 mph

Murphstock · Jul 7, 2011, 06:08 PM

Speed = Distance x Time.

ballengerb1 · Jul 7, 2011, 06:12 PM

There you have it, two totally different answers because we each read your question differently. Why not give us your data and then we can actually see what youn are doing

ebaines · Jul 8, 2011, 08:49 AM

The average speed is NOT simply the average of the individual speeds, unless the time spent traveling at each speeed is the same. In general you must calculate the total distance traveled and divide by the total time. For example, to use ballengerb1's numbers: if you travel 100 miles at 100MPH, 100 miles at 200MPH, and 100 miles at at 225 MPH then the total distance traveled is 300 miles, and the time taken is 100 mile/100MPH + 100 miles/200 MPH + 100 miles/225MPH = 1.944 hours. So the average speed is 300 miles/1.944 hours = 154.29 MPH.

The general formula is:

$ V_{avg} = \frac {(V_1 T_1 + V_2 T_2 + ... + V_n T_n)}{ (T_1 + T_2 + ... + T_n)} $

which is equivalent to:

$ V_{avg} = \frac {D_1 + D_2 + ...D_n} {D_1/V_1 + D_2/V_2 + ... + D_n/V_n)} $

dhicks88 · Apr 12, 2012, 04:16 PM

Drove 600 miles from his home. On the way back home he averaged 10 MPH less and the drive took him 2 hours longer. What was the average speed

ebaines · Apr 13, 2012, 06:32 AM

Please don't tack a new question onto an old one - you should start a new thread instead.

But to get you started: use the formula distance = velocity times time:

$ D=V \times T $

You can set up two equations:

$ D=T_1 \times v_1\\ T_1 \times v_1 = T_2 \times V_2 $

You are told that $D = 600, \ T_2 = T_1 + 2,$ and $V_2 = V_1 -10$ . Substitute these into the above equations and you get two equations in two unknowns . Now solve for $V_1$ [ and $T_1$ .