解：设从甲地到乙地的上坡路有$x\ \mathrm {km}，$平路有$y\ \mathrm {km}，$根据题意，得
$\{\begin{array}{l}{\frac {x}{3}+\frac {y}{4}=\frac {40}{60}}\\{\frac {y}{4}+\frac {x}{5}=\frac {30}{60}}\end{array}.$
解得
$\{\begin{array}{l}{x=\frac {5}{4}}\\{y=1}\end{array}.$
所以$x+y=\frac {5}{4}+1=\frac {9}{4}.$
答：甲地到乙地全程$\frac {9}{4}\ \mathrm {km}.$
