Question

In a primary school, the average weight of male students is 65.9 kg and the average weight of female students is 57 kg. If the average weight of all the students (both male and female) is 60.3 kg and the number of male students in the school is 66, then what is the number of female students in the school?

• A. 154
• B. 162
• C. 168
• D. 180
• E. 112

Answer 1

The correct option is E 112

The average weight of male students = 65.9 kg.
The average weight of female students = 57.0 kg.
The average weight of total students = 60.3 kg.
Let the total number of students= x,
Then, $\frac{65.9\times 66+(x-66)\times 57}{x}=60.3$.
$=65.9\times 66+57x-57\times 66=60.3x=(65.9-57)\times 66=3.3x=8.9\times 66=3.3x\Rightarrow 178=x$.
$\therefore$ Number of female students = 178 - 66 = 112.