<p>Your</a> question.</p>
<p>You can find various approaches to a similar question in Blue Book p.412 #18 in [url=<a href="http://talk.collegeconfidential.com/showthread.php?t=134898%5DUpdated">http://talk.collegeconfidential.com/showthread.php?t=134898]Updated</a> Consolidated List of Blue Book Math Solutions<a href="look%20for%20412%20/%2018%20/">/url</a>.
One of them: following xiggi advice, memorize a formulla for an average speed on two equal segments
2 * speed1 * speed2 / (speed 1 + speed 2).</p>
<p>So in 10 hours Juanita covered 10hr * 2 * 2km/hr * 3km/hr / (2km/hr + 3km/hr) = 24 km (up and down).
Half of that distance is the answer: 24/2 = 12 km.</p>