Answer
Total salary over 20 years = 793,582.9
Work Step by Step
Salary on first month $a_{1}$ = 24000
As salary increase 5% each year means the salary multiply by 1.05 each year, so common ratio = 1.05
Total salary calculated for 20 years then n = 20
Total salary over n years is given by sum formula $S_{n}$ = $a_{1}$$\frac{(1 - r^{n})}{(1 - r)}$
Total salary over 20 years $S_{20}$ = 24000$\frac{(1 - 1.05^{20})}{(1 - 1.05)}$
= 24000$\frac{(1 - 2.6533)}{(1 - 1.05)}$
= 24000$\frac{(-1.6533)}{(-.05)}$
= 24000$\times$33.065 = 793,582.9
