A graduate's starting salary is ₦120,000 per month and it increases by 5% at the beginning of each new year of service. What is the monthly salary during the fourth year?

The salaries form a geometric progression with $a = 120{,}000$ and $r = 1.05$. The fourth-year salary is the fourth term, $ar^3 = 120{,}000 \times 1.05^3 = 120{,}000 \times 1.157625 = 138{,}915$. Applying the increase four times, $ar^4$, gives about ₦145,861, which is the fifth-year salary.