Answer: 21%

Explanation:
Cost Price of 1 item = Rs. 10/11 and Selling Price of 1 item = Rs. 11/10
Profit = 11/10 – 10/11 = 121 – 100 / 110 = Rs. 21/110
Profit Percentage = (21/110) / (10/11) × 100 = 21/110 × 11/10 × 100 = 21%

Answer: 8% 

Explanation:
Let x eggs be bought at 4 for Rs 5
CP of x eggs = 5x / 4
Let another x eggs be bought at 9 for Rs. 10
CP of x eggs = 10x/9
Total CP of 2x eggs = 5x/4 + 10x / 9 = 85 / 36x = 2.3611x
Number of broken eggs = 0.15(2x) = 0.3x
Balance eggs = 2x – 0.3x = 1.70x
SP of 2 eggs = Rs. 3
SP of 1.7x eggs = (3 × 1.7x)/2×2.55x
Profit = (2.55 – 2.3611)x = 0.189x
Profit Percentage = 0.189x / 2.311x × 100 = 8% 

Answer: Rs. 72

Explanation:
Marked price = 80
Discount = 10 / 100 × 80 = Rs. 8
Selling Price = 80 – 8 = Rs. 72

Answer: Rs. 25

Explanation:
 Let the Cost Price = Rs x.
Profit = 20%
SP = CP(100 + gain% / 100) = x(12/100) = 12x/10
If CP = 0.8x and SP = 12x / 10 – 5
Then gain percentage = 25, i.e 25 = (12x/10 -5 -8x/10) / 8/10x × 100
2x = 4x – 50
i.e. 2x = 50
Cost price of the pen = Rs 25

Answer: 200

Explanation:
Let the original price be rs x
Increase = rs 0.3x
x+0.3x = 260x = 200

Answer: 0%

Explanation:
Let the price of fan b initially be rs x
Price of fan a initially is rs 2x
Increase in the price of a = 10/200 * (2x) = rs 0.2x
Decrease in the price of b = 20/100 *(x) = rs 0.2x
As the increase equals the decrease, the sum of the prices does not change.
There fore the required change is 0%

Answer: 50%

Explanation:
Profit = rs 300
Profit percentage = (300/600)(100%) = 50%

Answer: Rs 65

Explanation:
Let the cost price of the item be rs x
Profit = 0.2x
X + 0.2x = 60
X = 50
To gain 30% profit must be rs 0.3x
Hence, selling price must be rs 1.3x
= rs 65

Answer: 5% profit

Explanation:
Suppose 2 articles have the same cost price and one is sold at x% profit and the other is sold at y % loss. The overall profit/loss percentage is given by ½(difference of x and y)%
X=20
Y = 10
Overall profit/loss % = 5% profit

Answer: 40%

Explanation:
Let the initial cost be rs 100
It went up by 40% i.e new cost price = rs 140
Initial selling price = rs 120
Present selling price = 140 (1.2) = rs 168
Percentage increase in selling price = (168-120) / 120 * 100
= 40%