Answer: Option A. -> Rs. 400
$$\eqalign{
& {\text{Single discount = 50}}\% \cr
& {\text{Two successive discount}} \cr
& {\text{ = 40}} + {\text{10}} - \frac{{40 \times 10}}{{100}} \cr
& = 50 - 4 \cr
& = 46 \cr
& {\text{Difference}} \cr
& = 50 - 46 \cr
& = 4\% \cr
& {\text{Difference amount }} \cr
& {\text{ = 4}}\% {\text{ of 10000}} \cr
& {\text{ = }}\frac{4}{{100}} \times 10000 \cr
& {\text{ = Rs}}{\text{. 400}} \cr} $$

Answer: Option A. -> Rs. 72.20
Marked price of article = Rs. 80
$$\eqalign{
& {\text{Two successive discount }} \cr
& {\text{ = 5}} + 5 - \frac{{5 \times 5}}{{100}} \cr
& = 10 - 0.25 \cr
& = 9.75\% \cr
& {\text{Discount of article }} \cr
& {\text{ = 9}}{\text{.75% of 80}} \cr
& {\text{ = }}\frac{{9.75}}{{100}} \times 80 \cr
& = {\text{Rs}}{\text{. 7}}{\text{.80}} \cr
& {\text{Selling price of article }} \cr
& {\text{ = }}80 - 7.80 \cr
& {\text{ = Rs}}{\text{. 72}}{\text{.20}} \cr} $$

Answer: Option C. -> $$33\frac{1}{3}\% $$
Market price of dining table = Rs. 3000
After discount, cost price
$$\eqalign{
& {\text{ = 3000}} \times \frac{{90}}{{100}} \times \frac{{85}}{{100}} \cr
& {\text{ = Rs}}{\text{. 2295}} \cr} $$
After transport charges = 2295 + 105
$$\eqalign{
& {\text{Cost price = Rs}}{\text{. 2400}} \cr
& {\text{Selling price = Rs}}{\text{. 3200}} \cr
& {\text{Profit }}\% {\text{ }} \cr
& = \frac{{3200 - 2400}}{{2400}} \times 100 \cr
& = \frac{{800 \times 100}}{{2400}} \cr
& = 33\frac{1}{3}\% \cr} $$

Answer: Option C. -> 2%
Let the cost price = Rs. 100
$$\eqalign{
& {\text{Market price }} \cr
& {\text{ = 120}}\% {\text{ of 100 }} \cr
& {\text{ = Rs}}{\text{. 120}} \cr
& {\text{Selling price }} \cr
& {\text{ = 85}}\% {\text{ of 120 }} \cr
& {\text{ = }}\frac{{85}}{{100}} \times {\text{120 }} \cr
& {\text{ = Rs}}{\text{. 102}} \cr
& {\text{Gain }}\% = \frac{{102 - 100}}{{100}} \times 100 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 2\% \cr} $$

Answer: Option C. -> 15%
Marked price of machine = Rs. 6800
After 1st discount
$$\eqalign{
& = \frac{{90}}{{100}} \times 6800 \cr
& = {\text{Rs}}{\text{. 6120}} \cr} $$
Selling price of machine = Rs. 5202
$$\eqalign{
& {\text{Discount }}\% \cr
& = \frac{{6120 - 5202}}{{6120}} \times 100 \cr
& = \frac{{918}}{{6120}} \times 100 \cr
& = 15\% \cr} $$

Answer: Option D. -> $${\text{Rs}}{\text{. 322}}\frac{2}{9}$$
Let the marked price of an item = Rs. x
Selling price of an item $$ = \left( {100 - 24\frac{1}{2}} \right)\% \,{\text{of }}x$$
$$\eqalign{
& \Rightarrow 1510 = \frac{{151}}{2} \times \frac{1}{{100}} \times x \cr
& \Rightarrow x = {\text{Rs}}{\text{. 2000}} \cr
& {\text{Cost price of an item }} \cr
& = 1510 \times \frac{{100}}{{90}} \cr
& {\text{ = Rs}}{\text{. }}\frac{{15100}}{9} \cr
& {\text{Without discount, gain}} \cr
& {\text{ = }}2000 - \frac{{15100}}{9} \cr
& = \frac{{18000 - 15100}}{9} \cr
& = \frac{{2900}}{9} \cr
& = {\text{Rs}}{\text{. 322}}\frac{2}{9} \cr} $$

Answer: Option C. -> Rs. 64239
$$\eqalign{
& {\text{Net selling price }} \cr
& {\text{ = }}\frac{{92}}{{100}} \times \frac{{95}}{{100}} \times \frac{{98}}{{100}} \times 75000 \cr
& = {\text{Rs}}{\text{. 64239}} \cr} $$

Answer: Option C. -> Rs. 71.25
Market price of shoes = Rs. 475
$$\eqalign{
& {\text{Discount}} = \frac{{15}}{{100}} \times 475 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{285}}{4}{\text{ }} \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\text{ = Rs 71}}{\text{.25}} \cr} $$

Answer: Option C. -> 8.33%
Let original cost price = 100 units
$$\eqalign{
& {\text{Cost price of Balaji }} \cr
& {\text{ = 100}} \times \frac{{150}}{{100}} \times \frac{{80}}{{100}} \cr
& {\text{ = 120 units}} \cr
& {\text{Selling price of Balaji }} \cr
& {\text{ = }}\frac{{130}}{{100}} \times 100\, \cr
& {\text{ = 130 units}} \cr
& {\text{Profit of Balaji }} \cr
& {\text{ = 130}} - 120 \cr
& = {\text{10 units}} \cr
& {\text{Profit percent }} \cr
& {\text{ = }}\frac{{10}}{{120}} \times 100 \cr
& {\text{ = 8}}{\text{.33}}\% \cr} $$
Note: There is no use of Rs. 20 given in the question

Answer: Option B. -> Rs. 380
$$\eqalign{
& {\text{Cost price of the article}} \cr
& {\text{ = 500}} \times \frac{{95}}{{100}} \times \frac{{100}}{{125}} \cr
& = {\text{Rs}}{\text{. 380}} \cr} $$