A dishonest dealer sells his goods at 20% loss on the cost price but uses a faulty weight that weighs 25% less. His profit or loss percentage (rounded off to 2 decimal places) is:

To find the dealer's overall profit or loss percentage, we can break down the transaction by analyzing the cost price and the selling price for a standard quantity of goods.

Let us assume that the cost price (CP) of 100 grams of goods is 100 rupees.
This means:
Cost Price of 1 gram = 1 rupee.

According to the problem, the dealer sells his goods at a 20% loss on the cost price.
The selling price (SP) of 100 grams of goods would be:
$\mathrm{SP\; of\; 100\; grams}=100-(20\%\text{of}100)=80\text{rupees.}$

However, the dealer uses a faulty weight that weighs 25% less than the actual amount.
So, when a customer buys what is supposed to be 100 grams of goods, the dealer actually gives them:
$100-(25\%\text{of}100)=75\text{grams.}$

This means the dealer receives 80 rupees (the selling price he set for 100 grams) by giving only 75 grams of goods.
Therefore, the selling price of 75 grams of goods is 80 rupees.

Let us calculate the actual cost price (CP) of the 75 grams of goods that the dealer actually gave:
Since the cost price of 1 gram is 1 rupee, the cost price of 75 grams is:
$\mathrm{Actual\; CP}=75\text{rupees.}$

Now, we compare the actual cost price and the actual selling price for the 75 grams of goods:
Actual Cost Price (CP) = 75 rupees
Actual Selling Price (SP) = 80 rupees

Since the selling price is greater than the cost price, the dealer makes a profit.
Profit = Selling Price - Cost Price
$\mathrm{Profit}=80-75=5\text{rupees.}$

The profit percentage is calculated on the actual cost price:
$\mathrm{Profit\; Percentage}=\left(\frac{\mathrm{Profit}}{\mathrm{Actual\; CP}}\right)\times 100$
$\mathrm{Profit\; Percentage}=\left(\frac{5}{75}\right)\times 100$
$\mathrm{Profit\; Percentage}=\left(\frac{1}{15}\right)\times 100=\frac{20}{3}\%\approx 6.67\%$

Thus, the dealer makes a profit of 6.67%.