To find out how much more the Brandywine River needs to rise to reach the major flood stage of 13 ft, we'll start with the current flood stage of 9 ft and add the additional measurements of rise.
First, let's start with the initial rise of \(1 \frac{1}{12}\) ft:
\[ 1 \frac{1}{12} = \frac{12}{12} + \frac{1}{12} = \frac{13}{12} \]
Next, we add the second rise of \(1 \frac{5}{12}\) ft:
\[ 1 \frac{5}{12} = \frac{12}{12} + \frac{5}{12} = \frac{17}{12} \]
Now we add these rises to the flood stage:
- Calculate the total rise:
\[ \frac{13}{12} + \frac{17}{12} = \frac{13 + 17}{12} = \frac{30}{12} \]
This can be simplified:
\[ \frac{30}{12} = \frac{5}{2} = 2 \frac{1}{2} \]
- Now, add this rise to the original flood stage of 9 ft to find the current river height:
\[ 9 + 2 \frac{1}{2} = 9 + 2.5 = 11.5 \text{ ft} \]
- Finally, we calculate how much more the river needs to rise to reach the major flood stage of 13 ft:
\[ 13 - 11.5 = 1.5 \text{ ft} \]
Converting \(1.5\) ft to a fraction gives us:
\[ 1.5 = \frac{3}{2} \]
Thus, the Brandywine River needs to rise \(\frac{3}{2}\) ft (or 1 1/2 ft) more to reach the major flood stage of 13 ft.
The answer is:
\[ \frac{3}{2} \text{ ft} \]
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