Question : The average age of 25 girls in a class is 11.2 years and that of the remaining 15 girls is 10 years. Find the average age of all the girls in the class.
Option 1: 10.75 years
Option 2: 11.35 years
Option 3: 10.45 years
Option 4: 11.05 years
Correct Answer: 10.75 years
Solution :
The total age of the 25 girls = 25 × 11.2 = 280 years
The total age of the remaining 15 girls = 15 × 10 = 150 years
So, the total age of all the girls = 280 + 150 = 430 years
The total number of girls = 25 + 15 = 40
Therefore, the average age of all the girls in the class = $\frac{430}{40}$ = 10.75 years
Hence, the correct answer is 10.75 years.
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