$c$ and $d$ are inversely proportional and are both positive. The equation of proportionality is $c=\frac{5}{d}$. a) Does $c$ increase or decrease if $d$ increases? b) Does $d$ increase or decrease if $c$ increases?

Step 1 ：Given that $c$ and $d$ are inversely proportional and are both positive, the equation of proportionality is $c=\frac{5}{d}$.

Step 2 ：In an inverse proportion, as one quantity increases, the other decreases.

Step 3 ：So, if $d$ increases, $c$ should decrease. Similarly, if $c$ increases, $d$ should decrease.

Step 4 ：Final Answer: a) If $d$ increases, $c$ \(\boxed{decreases}\). b) If $c$ increases, $d$ \(\boxed{decreases}\).