Mike deposited ＄$$10000$$ in the bank. He earned an interest of＄$$2100$$ at the end of the second year. What is the interest rate per year of this bank? 
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Suppose the interest rate is $$m$$:  $$\begin{eqnarray}10000\times \left( 1+m \right)\times \left( 1+m \right)\&=\&10000+2100 \textbackslash\textbackslash{} m\&=\&0.1 \end{eqnarray}$$ 