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JAMB Mathematics 2020 Paper

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Question : 38

Total: 40

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

Solution:

x $\frac{\text{sumx}}{N}$

15 = $\frac{\text{sumx}}{N}$

$\text{sumx}$ = 15N........(i)

y = $\frac{\text{sumy}}{Ny} = \frac{\text{sumx} + 45}{N + 1}$

$\frac{18}{1} = \frac{15N + 45}{N + 1}$

18(N + 1) = 15N + 45

18N + 18 = 15N + 45

18N - 15N = 45 - 18

3N = 27

N = $\frac{27}{3}$

= 9

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