A tank is 25 m long, 12 m wide and 6 m deep. What is the cost of plastering of its walls and bottom at the rate of 75 paise per sq. m?

On my sister's 15th birthday, she was 159 cm in height, having grown 6% since the year before. How tall was she the previous year?

Find the total number of ways in which a black square and a white square can be selected from a chessboard such that both the squares lie either in the same row or in the same column.