## Calculus (3rd Edition)

$\frac{5}{2}$
According to the chain rule, $(g(f(x)))'=g'(f(x))\times f'(x)$ Then, $\frac{d}{dx}(g(f(x))|_{x=1}=g'(f(1))\times f'(1)$ $=g'(4)\times5=\frac{1}{2}\times5=\frac{5}{2}$