Question

there were 15 students in a class. when the ages of a teacher and anew boy are added, the average age of the class increases by 10 per cent while it remains the same when only the age of a boy is added. if the teacher’s age is eight more than twice the age of the new boy, then find the initial average age of the class

Answer 1

average of 15 students  = a

Total age of 15 student = a x 15 = 15a

Average of 16 students = a

Age of now child is = 16a - 15a = a

Teacher's age = 2a + 8

Average of 17 people = (16a + 2a + 8)/17  = (18a + 8)/17

ie.   (18a + 8) / 17  x  100   = 110

          a

(18a + 8) x 100 = 110a x 17

1800a + 800 = 1870a

1870 a - 1800a = 800

70a = 800

a = 800/70 = 11.43

Initial average = 11.4