Past papers › JAMB 2004 · UME › Question 43 Question JAMB General Maths 2004 Objective Statistics: data & averages Statistics: data & averages
The mean age of a group of students is 15 years. When the age of a teacher, 45 years old, is added, the mean becomes 18 years. Find the number of students in the group.
Worked solution (try it first) Let there be
n n n students.
Their total age is
15 n 15n 15 n .
With the teacher it is
15 n + 45 15n + 45 15 n + 45 for
n + 1 n + 1 n + 1 people.
The new mean is 18, so
15 n + 45 = 18 ( n + 1 ) = 18 n + 18 15n + 45 = 18(n + 1) = 18n + 18 15 n + 45 = 18 ( n + 1 ) = 18 n + 18 .
Collect terms:
27 = 3 n 27 = 3n 27 = 3 n , so
n = 9 n = 9 n = 9 , option B.
Watch out
With the teacher there are n + 1 n + 1 n + 1 n n n 15 n + 45 = 18 n 15n + 45 = 18n 15 n + 45 = 18 n n = 15 n = 15 n = 15 Report a problem with this question