To determine the weight of the uncooked brisket that Jeremiah needs, we start by noting that the brisket loses 35% of its weight during cooking. This means that he retains 65% of the uncooked weight after cooking.
Let's denote the weight of the uncooked brisket as \( x \). After cooking, he will have:
\[ 0.65x \]
We want this cooked weight to equal 12.5 pounds, so we set up the equation:
\[ 0.65x = 12.5 \]
Now, we can solve for \( x \):
\[ x = \frac{12.5}{0.65} \]
Calculating that gives:
\[ x \approx \frac{12.5}{0.65} \approx 19.23076923076923 \]
Rounding this to the nearest tenth, we get:
\[ x \approx 19.2 \]
Therefore, the weight of the uncooked brisket that Jeremiah should start with is approximately 19.2 pounds.