A bank offers 5% compound interest per half year. A customer deposits Rs. 3200 each on 1st January and 1st July of a year. At the end of the year, the amount he would have gained by way of interest is:
A bookseller bought 500 text books for 20,000. He wanted to sell them at a profit so that he get 50 books free. At what profit percent should he sell them?