the average age of 25 students in a class is 12 years . 15 students whose average age is 10 years joined them . what is the present average age .
"explanation : solution : present average = ax + by / a + b = 25 * 12 + 15 * 10 / 25 + 15 years = 300 + 150 / 40 = > 450 / 40 = > 11.25 . answer : c"
subtract(add(add(multiply(25, 12), 15), 25), multiply(25, 12))