Cost price of 100 books is equal to the selling price of 60 books. The gain percent age/loss percentage is
पुस्तकों का लागत मूल्य 60 पुस्तकों के विक्रय मूल्य के बराबर है। लाभ अथवा हानि की प्रतिशतता है -

Options

A. 0.66
B. `66 2/3%`
C. `66 3/2 %`
D. 0.67

Explanation

To solve the problem, we need to find the gain or loss percentage when the cost price of 100 books is equal to the selling price of 60 books.

### Step-by-Step Solution:

1. **Define Variables:**
Let the cost price (CP) of one book be \( x \).
Therefore, the cost price of 100 books is:
\[ \text{CP of 100 books} = 100x \]

2. **Selling Price Calculation:**
Since the cost price of 100 books is equal to the selling price of 60 books, we can denote the selling price (SP) of one book as \( y \).
Thus, the selling price of 60 books is:
\[ \text{SP of 60 books} = 60y \]
Setting the two equal gives us:
\[ 100x = 60y \]

3. **Express Selling Price in terms of Cost Price:**
Rearranging the equation to find \( y \):
\[ y = \frac{100x}{60} = \frac{5x}{3} \]

4. **Calculate Gain or Loss:**
The gain or loss can be calculated using the formula:
\[ \text{Gain} = \text{SP} - \text{CP} \]
For one book:
\[ \text{Gain} = y - x = \frac{5x}{3} - x = \frac{5x}{3} - \frac{3x}{3} = \frac{2x}{3} \]

5. **Calculate Gain Percentage:**
The gain percentage is given by:
\[ \text{Gain Percentage} = \left( \frac{\text{Gain}}{\text{CP}} \right) \times 100 \]
Substituting the values we have:
\[ \text{Gain Percentage} = \left( \frac{\frac{2x}{3}}{x} \right) \times 100 = \left( \frac{2}{3} \right) \times 100 = \frac{200}{3} \approx 66.67\% \]

### Final Answer:
The gain percentage is approximately \( 66.67\% \).