Let \( x \) be the number of bottles in each pack.
Andre's total number of bottles can be expressed as: \[ 3x + 11 \] Jillian's total number of bottles can be expressed as: \[ 5x + 3 \]
Since Andre and Jillian purchased the same number of bottles, we can set their total bottle counts equal to each other: \[ 3x + 11 = 5x + 3 \]
Next, we can solve for \( x \). Start by rearranging the equation to isolate \( x \): \[ 3x + 11 - 3 = 5x \] \[ 8 = 5x - 3x \] \[ 8 = 2x \] \[ x = \frac{8}{2} = 4 \]
Now we have determined that each pack contains \( \boxed{4} \) bottles.
To verify, we can calculate the total number of bottles Andre and Jillian bought:
For Andre: \[ 3 \text{ packs} \times 4 \text{ bottles/pack} + 11 \text{ singles} = 12 + 11 = 23 \text{ bottles} \]
For Jillian: \[ 5 \text{ packs} \times 4 \text{ bottles/pack} + 3 \text{ singles} = 20 + 3 = 23 \text{ bottles} \]
Both totals are indeed 23, confirming that our solution is correct. Each pack contains \( \boxed{4} \) bottles.