Chapter 4 - Proportions, Percents, and Solving Inequalities - 4.2 - Percents and Problem Solving - Problem Set 4.2 - Page 156: 61

2.5 years are needed.

The interest formula is: I = P $\times$ r $\times$ t. To find the time needed to invest, or t, we divide I by P $\times$ r. So, t = $\frac{I}{P\ \times\ r}$ P = 2400 r = 5.5% = 0.055 I = 330 Substitute these values in the formula to obtain: t = $\frac{330}{2400\ \times\ 0.055}$ t = $\frac{330}{132}$ t = 2.5 years