It took Malcom 3.5 hours to drive from city A to city B. On his way back to city A, he increased his speed by 20 km per hour and it took him 3 hours.

a) Find the average speed for the whole journey.

Question

It took Malcom 3.5 hours to drive from city A to city B. On his way back to city A, he increased his speed by 20 km per hour and it took him 3 hours. 

a) Find the average speed for the whole journey.

anonymous · Answer

Average speed is $$
\frac{\Delta positon}{\Delta time} = \frac{distance\ traveled}{amount\ of\ time\ it\ took}
$$

anonymous · Answer

Which is...

anonymous · Answer

Hmm, well, come up with some variables...

anonymous · Answer

Say the traveled distance $d$ and the going there was speed $v$.

anonymous · Answer

$$
3.5v  = d = 3(v+20)
$$

anonymous · Answer

Got it. 129.2 km/hr        Right?

anonymous · Answer

Umm, not sure cause I haven't actually solved it yet.

anonymous · Answer

Hahahaa :D

anonymous · Answer

http://www.wolframalpha.com/input/?i=d+%3D+3.5v%3B+d%3D3w%3B+w%3D+v%2B20%3B+a+%3D+2d+%2F+%283.5%2B3%29

anonymous · Answer

The $a$ in there is my average velocity.