The mean age of a group of students is 15 years. When the age of a teacher, 45 years old, is added to the age of the students, the mean of their ages becomes 18 years. Find the number of the students in the group

  • A 9
  • B 7
  • C 42
  • D 15
jamb 2004mathematics

The correct answer is A. 9

Let's say the number of students in the group is x. The total age of the students is 15x.

When the teacher's age is added, the total age becomes 15x + 45. The new mean is 18, so we can write the equation (15x + 45)/(x + 1) = 18.

Solving for x, we get x = 9. So, there are 9 students in the group.

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