Time to earn a given interest

Statement

For how long must a capital of $600\ \text{€}$ be invested at $5\%$ annual simple interest to produce $45\ \text{€}$ of interest?

Solution

From $I = C\cdot r\cdot t$ we get $t = \dfrac{I}{C\cdot r}$. $t = \frac{45}{600\cdot 0{.}05} = \frac{45}{30} = 1{.}5\ \text{years} = \boxed{18\ \text{months}}.$