Sita purchased 10 books, 15 diaries, and 20 folders for Rs. 500, Rs. 1200, and Rs. 1000, respectively, from a seller. By selling each book and each diary, the seller made a profit of ‘e%’ and ‘f%’, respectively, such that f = 3e. Find the profit earned by the seller on selling all the folders given the condition that the cost price of a diary, a book, and a folder is the same.

According to the question Let the cost price of each book, each diary, and each folder be Rs. ‘z’ Selling price of each book = (500/10) = Rs. 50 Selling price of each diary = (1200/15) = Rs. 80 According to the question, (50–z)/z×100 = e…… (I) Also, (80–z)/z×100 = f…… (II) Use the given relationship [f = 3e] Dividing equation (I) by (II), we get 3(50 − z)=80 − z 150 − 3z = 80 − z 150 − 80 = 3z − z 70 = 2z z = (70/2) = 35 Cost Price of All Folders: Cost price of one folder = Rs. 35 Cost price of all 20 folders = Rs. 35 × 20 = 700 Calculate the Profit Earned on Selling All Folders: Selling price of all 20 folders = Rs. 1000 Profit = Selling price - Cost price = Rs.1000 − 700 = 300 The profit earned by the seller on selling all the folders is Rs. 300.