### Instruction: For two real values of $n$, the equation $4x^2+nx+25=0$ has exactly one solution in $x$. What is the positive value of $n$?### Response: I notice that this is a quadratic equation, and I know that it has exactly one solution in $x$ when the discriminant is zero.
The discriminant is the part under the square root in the quadratic formula, so I can write it as $n^2-4(4)(25)$.
Setting this equal to zero, I get $n^2=400$, which has two real solutions: $n=\pm 20$.
The problem asks for the positive value of $n$, so I choose $n=20$.