In June, Mr Tan saved 20% of his salary. In July, his monthly salary increased by $600 and he saved 15% of his new monthly salary. Given that Mr Tan saved the same amount of money in both months, find the percentage increase in Mr Tan's salary. Answer : ___

1. Form an equation based on the equal savings in both months

Let Mr Tan's salary in June be $x$.
Savings in June = $20\%$ of $x = 0.2x$
Salary in July = $x + 600$
Savings in July = $15\%$ of $(x + 600) = 0.15(x + 600)$
Since the savings are the same:
$0.2x = 0.15(x + 600)$

2. Solve the equation to find the June salary

$0.2x = 0.15x + 90$
$0.2x - 0.15x = 90$
$0.05x = 90$
$x = \frac{90}{0.05} = 1800$
Mr Tan's salary in June was $\char36{}1800$.

3. Calculate the percentage increase in his salary

Increase in salary = $\char36{}600$
Percentage increase = $\frac{\text{Increase}}{\text{Original Salary}} \times 100\%$
$= \frac{600}{1800} \times 100\%$
$= \frac{1}{3} \times 100\% = 33\frac{1}{3}\%$