Problem: the average age of 50 students in a class is 10 years . if teacher ' s age is also included then average increases 1 year then find the teacher ' s age ?
Rationale: "total age of 50 students = 50 * 10 = 500 total age of 51 persons = 51 * 11 = 561 age of teacher = 561 - 500 = 61 years answer is c"
annotated_formula: subtract(add(add(multiply(50, 10), 1), 50), multiply(50, 10))