List of top Mathematics for Economy Questions on Differential Calculus

Let f: [0,∞) → $\R$ be a function defined by $f(x)=\frac{x+1}{x+2}$ for all $x\isin\R$. Then f is

Let a,b $\epsilon$ R. If f(x)= ax+bis such that
a+b=4 and f(x + y) = f(x)+f(y)-2 for all x, y $\epsilon$ R,
then  $\sum_{n=1} ^{50} f(n)$ =__________  (in integer).