Let c be the cost of one guitar pick.
Therefore, the total cost of the 25 guitar picks is 25*c.
The cost of one guitar string is c+1.
The total cost of the 25 guitar strings is 25*(c+1).
The total cost of the purchases is 25*c + 25*(c+1) = 40.
Combining like terms, we get 50c + 25 = 40.
Subtracting 25 from both sides of the equation, we get 50c = 15.
Dividing both sides of the equation by 50, we get c =<<0.3=0.30>>0.30.
The cost of one guitar string is c+1 = 0.30+1 = <<0.30+1=1.30>>1.30. Answer: \boxed{1.30}.