The mean age group of some students is 15years. When the ...
The mean age group of some students is 15years. When the age of a teacher, 45 years old, is added to the ages of the students, the mean of their ages become 18 years. Find the number of students in the group.
7
9
15
42
Correct answer is B
x ∑xN
15 = ∑xN
∑x = 15N........(i)
y = ∑yNy=∑x+45N+1
181=15N+45N+1
18(N + 1) = 15N + 45
18N + 18 = 15N + 45
18N - 15N = 45 - 18
3N = 27
N = 273
= 9