## marihelenh one year ago A motorist drives 150 km from one city to another in 2.5 h but makes the return trip ikn only 2.0 h. What are the average speeds for (a) each half of the round trip and (b) the total trip.

1. marihelenh

@triciaal @amistre64

2. amistre64

what is your concept of an average speed?

3. marihelenh

What do you mean? I tried the problem and I got some answers, could you see if I am on the right path with this problem?

4. amistre64

solutions start with knowing what it is you are looking for ... in this case, it wants an average speed.

5. triciaal

distance between the cities stays the same

6. amistre64

we need to make sure we have a proper definition of average speed to get started

7. marihelenh

s=d/t

8. amistre64

more accurately I would say average speed = (distance covered)/(time it took)

9. amistre64

s (or speed) is an instantaneous measurement ...

10. marihelenh

|dw:1440972635400:dw|

11. amistre64

those are fine for part a, assuming the mathing is correct, structure is fine

12. marihelenh

For part (b) then, could I do, $\frac{ 150km +150km }{ 2.5h +2.0h }=\frac{ 300km }{ 4.5h }=66.6km/h=67km/h$

13. amistre64

you did fine

14. marihelenh

That's reassuring. Thank you. Can you see if you can help me with another? I am not quite sure how to do it. I kind of get one part, but don't understand it completely.

15. amistre64

i can put an eye to it ... then i might be able to determine how useful i can be

16. marihelenh

Ok, well just give me a minute.

17. amistre64

k