Subject: General Aptitude · Chapter: Average · Exam: 2008 · Marks: · Difficulty:
The average age of a class was 15 years. When 5 boys whose average age was 12 years 6 months were admitted in the class, the average was reduced by 6 months. How many students were there in the class originally?
Answer
Answer (as printed):
Explanation
Let the original number of students in the class be $x$. Then, $$15 x+12 \frac{1}{2} \times 5=14 \frac{1}{2}(x+5) \Rightarrow 15 x+\frac{25}{2} \times 5=\frac{29}{2} x+\frac{29}{2} \times 5 \Rightarrow \frac{x}{2}=10 \Rightarrow x=20 .$$ Hence, required number of students = 20.
Explanation as extracted from the printed page; notation may be imperfect.