Chapter 4 - Proportions, Percents, and Solving Inequalities - 4.2 - Percents and Problem Solving - Problem Set 4.2 - Page 156: 60

3000 dollars are needed as principal.

The interest formula is: I = P $\times$ r $\times$ t. To find the principal, or P, we divide I by r $\times$ t. So, P = $\frac{I}{r\ \times\ t}$ r = 5% = 0.05 t = 4 I = 600 Substitute these values in the formula to obtain: P = $\frac{600}{0.05\ \times\ 4}$ P = $\frac{600}{0.20}$ P = 3000 dollars.