jmc

Putting these fractions over a common denominator, we get $$\frac{1}{ab}+\frac{1}{ac}+\frac{1}{ad}+\frac{1}{bc}+\frac{1}{bd}+\frac{1}{cd}=\frac{cd+bd+ac+ad+ac+ab}{abcd}.$$By Vieta's formulas, $ab+ac+ad+bc+bd+cd=9$ and $abcd=4.$ Therefore, the answer is $\boxed{\frac{9}{4}}.$