Ken divides his monthly salary into daily expenses, spending and saving in the ratio 3:4:5 respectively. Later he decides to spend $1200 more daily the new ratio become 9:8:7.
Calculate his monthly salary. Answer ...

1. Write the original and new daily expenses as fractions of the monthly salary.

Original ratio: daily expenses : spending : saving $=3:4:5$

Total parts originally $=3+4+5=12$.

Original daily expenses $=\dfrac{3}{12}=\dfrac{1}{4}$ of the salary.

New ratio $=9:8:7$

Total parts now $=9+8+7=24$.

New daily expenses $=\dfrac{9}{24}=\dfrac{3}{8}$ of the salary.

2. Find the fraction of the salary represented by the increase of \$1200.

Increase in daily expenses
$=\dfrac{3}{8}-\dfrac{1}{4}$
$=\dfrac{3}{8}-\dfrac{2}{8}$
$=\dfrac{1}{8}$

So $\dfrac{1}{8}$ of the monthly salary is $1200.

3. Calculate the monthly salary.

Monthly salary
$=1200\times 8$
$=9600$