A shopkeeper purchased one dozen pens for Rs. 108 and sold these at Rs. 12.50 each.
find:
(i) the cost of one pen.
(ii) profit or loss on selling one pen.
(iii) his total profit or loss onselling all pens.

Answer

Let's solve the problem step by step.

### Step 1: Find the cost of one pen.
The cost price (CP) of one dozen pens is given as Rs. 108. Since one dozen equals 12 pens, we can find the cost price of one pen by dividing the total cost by the number of pens.

\[ \text{Cost Price of 1 pen} = \frac{\text{Total Cost Price of 12 pens}}{\text{Number of pens}} = \frac{108}{12} = 9 \text{ Rs.} \]

### Step 2: Find the selling price of one pen.
The selling price (SP) of one pen is given as Rs. 12.50.

### Step 3: Calculate the profit or loss on selling one pen.
To find the profit on selling one pen, we subtract the cost price from the selling price.

\[ \text{Profit on 1 pen} = \text{Selling Price} - \text{Cost Price} = 12.50 - 9 = 3.50 \text{ Rs.} \]

### Step 4: Calculate the total profit on selling all pens.
Since there are 12 pens, we can find the total profit by multiplying the profit on one pen by the total number of pens.

\[ \text{Total Profit} = \text{Profit on 1 pen} \times \text{Number of pens} = 3.50 \times 12 = 42 \text{ Rs.} \]

### Summary of Results:
(i) The cost of one pen is Rs. 9.
(ii) The profit on selling one pen is Rs. 3.50.
(iii) The total profit on selling all pens is Rs. 42.

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