If the cost price of 9 articles is equal to the selling price of 12 articles, what is the percentage of gain or loss?

Let's assume the cost price of each article is $1.

Cost price of 9 articles = 9 * $1 = $9
Selling price of 12 articles = 12 * $1 = $12

Since the selling price is greater than the cost price, there is a gain.

Gain = Selling price - Cost price
Gain = $12 - $9 = $3

Percentage of gain = (Gain / Cost price) * 100
Percentage of gain = ($3 / $9) * 100
Percentage of gain = 33.33%

Therefore, the percentage of gain is 33.33%.

Step 1: Calculate the cost price and selling price per article

- Let the cost price per article be x.
- Since the cost price of 9 articles is equal to the selling price of 12 articles, the selling price per article is 9x/12 = 3x/4.

Step 2: Calculate the percentage of gain or loss

- Percentage gain or loss = [(Selling price - Cost price) / Cost price] x 100
- Percentage gain or loss = [(3x/4 - x) / x] x 100
- Percentage gain or loss = [(x/4) / x] x 100
- Percentage gain or loss = (1/4) x 100
- Percentage gain or loss = 25%

Therefore, there is a 25% gain.