the average age of a class of 20 students is 18 years . the average increased by 2 when the teacher ' s age also included . what is the age of the teacher ?
"if age of the teacher was 18 , average would not have changed . since average increased by 2 , age of the teacher = 18 + 22 × 1 = 40 answer : a"
subtract(multiply(add(20, 2), add(18, 2)), multiply(20, 18))