2004
Mathematics
67ca00ce0c643c71d77dee1f
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.
0
B.
7
C.
42
D.
15
Correct Answer: 0
Explanation
Let the number of students = x Total age of the students = 15x Total age including age of the teacher = 15x + 45 Mean of their ages; (15x + 45)/(x + 1) = 18 = 15x + 45 = 18(x + 1) = 15x + 45 = 18x + 18 = 18x - 15x = 45 - 18 = 3x = 27 x = 9
Let the number of students = x Total age of the students = 15x Total age including age of the teacher = 15x + 45 Mean of their ages; (15x + 45)/(x + 1) = 18 = 15x + 45 = 18(x + 1) = 15x + 45 = 18x + 18 = 18x - 15x = 45 - 18 = 3x = 27 x = 9THIS WEEK's
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