13 articles were bought for Rs. 5980 and sold for Rs 6656. How much was the approximate profit percentage per article?

Anoop sells a book to Mayank at a profit of 20% and Mayank sells this book to Siddharth at a profit of 25%. Now Siddharth sells this book at a loss of 10% to Shishir. At what percentage loss should Shishir sells this book now so that his SP becomes equal to Anoop’s CP?

A used car dealer sells a car for Rs 7.6 lakhs and makes some loss. If he had sold if for Rs.9.2 lakhs his profit would been thrice of his loss. What was the cost price of the car (in Rs. Lakhs)? 

A shopkeeper has 11 books of same cost price. He sells the first book at certain price, then he sells second book at a price which is ₹ 1 less than the selling price of first book and then he sells third book at a price which is ₹1 less than the selling price of second book. Following this pattern, he sold all 11 books. If he sells sixth book at its cost price. Find the overall percent profit or loss on selling all 11 books.