Let the cost of one guitar pick be \( c \) dollars. According to the problem, the cost of one guitar string is \( c + 1 \) dollars.
Patrick purchased 25 guitar picks and 35 guitar strings. Therefore, the total cost of the guitar picks and strings can be expressed as:
\[ \text{Total cost} = (\text{Number of guitar picks} \times \text{Cost of one guitar pick}) + (\text{Number of guitar strings} \times \text{Cost of one guitar string}) \]
Substituting the values we have:
\[ \text{Total cost} = (25 \times c) + (35 \times (c + 1)) \]
The total cost is given as $40, so we can set up the equation:
\[ 25c + 35(c + 1) = 40 \]
Expanding the expression inside the parentheses gives us:
\[ 25c + 35c + 35 = 40 \]
Combining like terms:
\[ 60c + 35 = 40 \]
Next, we isolate \( c \) by subtracting 35 from both sides:
\[ 60c = 40 - 35 \]
\[ 60c = 5 \]
Now, divide both sides by 60 to solve for \( c \):
\[ c = \frac{5}{60} = \frac{1}{12} \]
Now that we have \( c \), we can determine the cost of one guitar string:
\[ \text{Cost of one guitar string} = c + 1 = \frac{1}{12} + 1 = \frac{1}{12} + \frac{12}{12} = \frac{13}{12} \]
Thus, the cost of one guitar string is:
\[ \boxed{\frac{13}{12}} \text{ dollars} \]
Alternatively, in decimal form, this is approximately $1.08.