Hi everybody.

I'm have some trouble with the speed= distance/time.
I think It's because it minutes, seconds and fractionsof a second, rather than hours and minutes.

2.8km takes 78.73seconds(1.18.73 ) what is the average speed?

2.8x10^3/78.73

speed=distance/time so speed=2.8km/78.73s=0.03556km/s

now if you want to convert to other units (say km/h) you can do it thusly:

\frac {2.8km} {78.73s} * \frac {60s} {1m} * \frac {60m} {1h} = \frac {128.0325km} {1h}

notice how you set up the units to cancel out and leave only the ones you're interested in?

let us know if you have more questions or if we haven't gotten to the root of your problem.

128.0325 Kilometers Per Hour?

Primitive Math:
1)60 X 60 =3600(Seconds in hour)
2)3600/78.73= 45.7259
3)45.7259 X 2.8 = 128.0325 Kmph