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
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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