<p>1.)</p>
<p>Suppose you travel d distance at r1 rate followed by d distance at r2 rate. </p>
<p>Generally, rate*time = distance so we spend two times in our situation above: one at r1 and one at r2. So,</p>
<p>t1 = d/r1 and t2 = d/r2</p>
<p>Total time = t1 + t2=d/r1 + d/r2
Total distance = d+d = 2d</p>
<p>Average rate = total distance/total time = 2d/( d/r1 + d/r2 ) = 2r1r2/(r1 + r2)</p>
<p>2.) We don’t have enough information to come up with an expression. You have to give a proportion of the two times to each other, or the two rates to each other.</p>