Step-by-step explanation and answers:
300 articles at a total cost of $1500:
$1500 / 300 = $5 / article
Sells 260 articles at a price 20% above this ^ price:
20% of $5 is $1, so $5 + $1 = $6
Then he sells 260 articles at the price of ^ $6
260 * $6 = $1560
Each of the remaining articles is sold at a price that's 50% of the 260 he sold.
He sold those for $6, so he would now sell the last 40 for $3
From the remaining 40 articles, he makes 40 * $3, or $120
The shopkeeper made $1560 + $120 = $1680, which is $180 more than he bought them for ($1500)
Therefore, he made a profit percentage of $180 / $1500, (the amount of profit over the amount spent).
He made a profit percentage, compared to the cost price, of 12%.
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