Solution:
According to the question,
Shopkeeper sells his goods at cost price
Let, Cost price of 1000 gm. goods = Rs. 1000
He sold 900 gm. goods
Selling price of 900 gm. goods = Rs. 1000
Cost price of 900 gm. goods = Rs. 900
$$\eqalign{ {\text{Profit}}\% = \frac{{100}}{{900}} \times 100 \cr \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 11\frac{1}{9}\% \cr} $$

Solution:
\[\begin{array}{*{20}{c}} {}{ + 16\% }{ - 12\% } \\ {}{\text{I}}{{\text{II}}} \\ {{\text{Cost Price}}}{{{25}_{ \times 22}}}{{{25}_{ \times 29}}} \\ {{\text{Profit/Loss}}}{{4_{ \times 22}}}{ - {3_{ \times 29}}} \\ {{\text{Sale Price}}}{{{29}_{ \times 22}}}{{{22}_{ \times 29}}} \end{array}\]
Cost Price = 25(29 + 22) = 25 × 51
Profit/Loss = 88 - 87 = +1
Profit % $$ = \frac{1}{{25 \times 51}} \times 100 = 0.08\% $$

Solution:
40% discount on 500 = $$\frac{{40 \times 500}}{{100}}$$  = Rs. 200 Two successive discount on 500, = 30% of 500 + 10% of (500 - 30% of 500) = 150 + 10% of 350 = 150 + 35 = Rs. 185 Difference in Discount = 200 - 185 = Rs. 15

Solution:
VAT % = 13.5%
Cost price (including VAT) = Rs. 6810
$$\eqalign{ \therefore {\text{List price}} = \frac{{6810}}{{113.5}} \times 100 \cr \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}{\text{. }}6000 \cr} $$