Solution:
Percentage of Non-tax paying employees
= (100 - 31)%
= 69%
69% of total employees = 20700
Total employees
= $$\frac{20700}{69}$$ × 100
= 30000

Solution:
No. of boys = 75% No. Girls = 25% = 420 Now comparing, 25% = 420 1% = $$\frac{{420}}{{25}}$$ So, 75% = $$\frac{{420 \times 75}}{{25}}$$  = 1260 No. of boys = 1260

Solution:
$$\eqalign{ 90\% \to 216 \cr 10\% \to 24 \cr 100\% \to \boxed{240} \cr} $$

Solution:
\[\begin{array}{*{20}{c}} {{\text{Income}}}{{\text{Expenditure}}}{{\text{Saving}}} \\ \begin{gathered} 600 \hfill \\ \,\,\,\,\,\,\,\,\,\,{ \downarrow ^{ + 10\% }} \hfill \\ 660 \hfill \\ \end{gathered} \begin{gathered} 500 \hfill \\ \,\,\,\,\,\,\,\,\,{ \downarrow ^{ + 20\% }} \hfill \\ 600 \hfill \\ \end{gathered} \begin{gathered} 100 \hfill \\ \hfill \\ 60 \hfill \\ \end{gathered} \end{array}\]
Decrease in saving = $$\frac{{40}}{{100}}$$ × 100 = 40%

Solution:
$$\eqalign{ {\text{Let number of men in the population be }}x \cr {\text{Number of women}} = \left( {35000 - x} \right) \cr {\text{Increase in the number of men}} \cr = 6\% \,of\,x = \frac{{6x}}{{100}} \cr {\text{Increase in the number of women}} \cr = \left( {3500 - x} \right) \times \frac{4}{{100}} \cr {\text{Increase in whole population}} \cr = 36760 - 35000 = 1760 \cr {\text{Now}}, \cr \frac{{6x}}{{100}} + \left[ {\left( {35000 - x} \right) \times \frac{4}{{100}}} \right] = 1760 \cr \left[ {\left( {6x - 4x} \right) + 35000 \times \frac{4}{{100}}} \right] = 1760 \cr 2x + 35000 \times 4 = 1760 \times 100 \cr 2x = 176000 - 35000 \times 4 \cr x = 18000 \cr {\text{Number}}\,{\text{of}}\,{\text{men}} = 18000 \cr {\text{Number}}\,{\text{of}}\,{\text{women}} \cr = 35000 - 18000 \cr = 17000 \cr} $$

Solution:
Let Rs. 100 be spend on rice initially for 20 kg. As the price falls by 20%, new price for 20 kg rice,= (100 - 20% of 100) = 80 New price of rice = $$\frac{{80}}{{20}}$$ = Rs. 4 per kg. Rice can bought now at = $$\frac{{100}}{{4}}$$ = 25 kg.

Solution:
(7.9% of 134) - (3.4% of 79)
$$ = \left( {\frac{{79}}{{10}} \times \frac{1}{{100}} \times 134} \right) - $$     $$\left( {\frac{{34}}{{10}} \times \frac{1}{{100}} \times 79} \right)$$
$$\eqalign{ = \frac{{79}}{{1000}} \times \left( {134 - 34} \right) \cr = \frac{{79}}{{1000}} \times 100 \cr = \frac{{79}}{{10}} \cr = 7.9 \cr} $$