The method of soil conservation in which stones, grass, soil are used to build barriers along contours and trenches are made in front of the barriers to collect water is called?
In a certain code language, '+' represents 'x', '-' represents '+', 'x' represents '÷' and '÷' represents '-'. What is the answer to the following question?
The average height of 50 bats is 126 cm. Some bats of average height 120 cm are removed. If the new average height is 130 cm, then how many bats are remaining?