To find the percentage of packs that contained mint-flavored gum, we first need to determine the total number of packs produced.
The total number of packs is: \[ 29 \text{ (mint packs)} + 71 \text{ (fruit packs)} = 100 \text{ packs} \]
Next, we find the percentage of the packs that contained mint-flavored gum: \[ \text{Percentage of mint packs} = \left( \frac{\text{Number of mint packs}}{\text{Total number of packs}} \right) \times 100 \]
Substituting the values: \[ \text{Percentage of mint packs} = \left( \frac{29}{100} \right) \times 100 = 29% \]
Thus, the percentage of the packs that contained mint gum is: \[ \boxed{29%} \]