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.
-
A.
7 -
B.
9 -
C.
15 -
D.
42
Correct Answer: Option B
Explanation
x (frac{sum x}{N})
15 = (frac{sum x }{N})
(sum x) = 15N……..(i)
y = (frac{sum y}{Ny} = frac{sum x + 45}{N + 1})
(frac{18}{1} = frac{15N + 45}{N + 1})
18(N + 1) = 15N + 45
18N + 18 = 15N + 45
18N – 15N = 45 – 18
3N = 27
N = (frac{27}{3})
= 9
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