  A convex function $f:[a,b]\to\mathbb{R}$ satisfies the so-called
Hermite-Hadamard inequality $$ f\left(\frac{a+b}{2}\right)\leq
\frac{1}{b-a}\int_a^{b}f(t)dt\leq \frac{f(a)+f(b)}{2}. $$ Motivated by the
above estimates, in this paper we consider approximately monotone and convex
functions, and give upper and lower bounds to the numerical integral mean,
i.e., to $\frac1{b-a}\mathcal{I}_{n}(f)$, where $\mathcal{I}_{n}(f)$ denotes
some of the most popular Newton-Cotes quadrature formulas.
