In a primary school the average weight of male students..

Let the number of female students be x Let weight of female students = 57x Number of male students = 66 Total weights of male students = 65.9 × 66 Average weight of all the students = 60.3 kg Total weights of all the students = 60.3 (66 + x) According to given information, Then, $\begin{array}{l}\text{⇒ 60.3 (66 + x) = 66 × 65.9 + 57x}\\ \text{⇒ 60.3 × 66 + 60.3x = 66 × 65.9 + 57x}\\ \text{⇒ 60.3x – 57x = 66 (65.9 – 60.3)}\\ \text{⇒ 3.3x = 66 × 5.6}\\ \begin{aligned}\therefore&\mathrm{x}=\frac{66\times5.6}{3.3}\\ \Rightarrow&\mathrm{x}=2\times56\\ \Rightarrow&\mathrm{x}=112\end{aligned}\end{array}$