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.
Take Free Practice Test On 2026 JAMB UTME, Post UTME, WAEC SSCE, GCE, NECO SSCE
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
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