Answer: Option A. -> 11$1/9$%
Answer: (a)Marked price = Rs.xDiscount = Rs.$x/5$S.P. = $x - x/5 = Rs.{4x}/5$Loss = Rs.$x/10$C.P. = ${4x}/5 + x/10$= ${8x + x}/10 = Rs.{9x}/10$Loss per cent = ${x/10}/{{9x}/10} × 100$= $100/9 = 11{1}/9$%

Answer: Option B. -> 30%
Answer: (b)C.P. of article = Rs.100Let marked price of article x.$x × 90/100 = 117$$x = {117 × 100}/90$= Rs.130 or 30% above the cost price.Using Rule 8,Here, $r_1$ = 10%, gain % = 17%, r = ?Gain % = ${r × (100 - r_1)}/100 - r_1$17 = ${r × (100 - 10)}/100 - 10$27 = ${r × 90}/100$ ⇒ r = 30%

Answer: Option C. -> 19%
Answer: (c)Let the C.P. of each article be Rs.100.Marked price = Rs.140S.P. = ${140 × 85}/100$ = Rs.119Gain per cent = 19%Using Rule 8,Here, r = 40%, $r_1$ = 15%Gain % = ${r × (100 - r_1)}/100 - r_1$= ${40 × (100 - 15)}/100 - 15$= ${40 × 85}/100 - 15$= $3400/100$ - 15 = 19%

Answer: Option B. -> 8%
Answer: (b)Gain % = $20 - 10 - {20 × 10}/100$= 20 - 12 = 8%Using Rule 8,Here, r = 20%, $r_1$ = 10%Profit or loss= ${r × (100 - r_1)}/100 - r_1$= ${20 × (100 - 10)}/100 - 10$= 18 - 10 = 8% profit.

Answer: Option A. -> Rs.3,500
Answer: (a)Marked price of article = Rs.x (let)S.P. of article= Rs.$(x × 90/100 × 108/100)$$x × 90/100 × 108/100$ = 3402$x = {3402 × 100 × 100}/{90 × 108}$$x$ = Rs.3500

Answer: Option B. -> 2%
Answer: (b)If the C.P. of goods be Rs.100, thenMarked price = Rs.120S.P. = ${120 × 85}/100$ = Rs.102Hence, Profit per cent = 2% Using Rule 8,A tradesman marks his goods r% above his cost price. If he allows his customers a discount of $r_1$% on the marked price. Then is profit or loss per cent is${r × (100 - r_1)}/100 - r_1$(Positive sign signifies profit and negative sign signifies loss).

Answer: Option D. -> 20%
Answer: (d)S.P. for a profit of 12%= ${8000 × 112}/100$ = Rs.8960Discount = 11200 - 8960 = Rs.2240If the discount per cent be x, then${11200 × x}/100 = 2240$$x = {2240 × 100}/11200 = 20%$Using Rule 6,Here, M.P. = Rs.11200, C.P. = Rs.8000r =12% D = x%$\text"MP"/\text"CP" = {100 + r}/{100 - D}$$11200/8000 = {100 + 12}/{100 - x}$= $11200/8000 = 112/{100 - x}$100 - x = 80 ⇒ x = 20%

Answer: Option C. -> 20%
Answer: (c)Marked price = Rs.690Discount = 10%SP = ${690 × 90}/100$ = Rs.621Profit = 8%CP = $621/108 × 100$ = Rs.575Profit without discount= 690 - 575 = Rs.115Profit per cent= $115/575 × 100$ = 20%Using Rule 9,The marked price of an article is fixed in such a way that after allowing a discount of r% a profit of R% is obtained. Then the marked price of the article is $({r + R}/{100 - r} × 100)$% more than its cost price.

Answer: Option B. -> 60%
Answer: (b)Let C.P.of article = Rs.100If the marked price of article be x, then$x × 75/100$ = 120$x = {120 × 100}/75$ = 160i.e. 60% above the cost priceUsing Rule 9,r = 25%, R = 20%Required percentage= $({r + R}/{100 - r} × 100)$%= $({25 + 20}/{100 - 25} × 100)$%= $45/75 × 100$ = 60%

Answer: Option D. -> 20%
Answer: (d)Let CP of radio be Rs.x.According to the question,${108x}/100 = 4800 × 90/100 = 4320$$x {4320 × 100}/108$ = Rs.4000If no discount is allowed,Gain per cent= $800/4000 × 100 = 20%$Using Rule 6,M.P. = Rs.4800, D = 10%, r = 8%$\text"MP"/\text"CP" = {100 + r}/{100 - D}$$4800/\text"CP" = {100 + 8}/{100 - 10}$C.P. = ${4800 × 90}/108$C.P. = 4000Gain % (without discount)= ${4800 - 4000}/4000 × 100$= $800/4000 × 100$ = 20%