Markov’s Inequality

For any random variable $X$ which only takes non-negative values, and any positive $t$, $$\mathrm{Pr}[X \geq t]\leq \frac{\mathbb{E}[X]}{t}$$

equivalently, $$\mathrm{Pr}[X \geq \alpha\cdot\mathbb{E}[X]]\leq\frac{1}{\alpha}$$

Example of Concentration inequality