The average mass of 3 girls and 4 boys is 35.2 kg. If the total mass of the boys is 158.2 kg. Find the mass of the girls.

Hi Xin,
Please find below the solution to the asked query :

$$\begin{gathered} \mathrm{We} \mathrm{have}, \\ \mathrm{average} \mathrm{mass} \mathrm{of} 3 \mathrm{girls} \mathrm{and} 4 \mathrm{boys} = 35.2 \mathrm{kg} \\ \Rightarrow \frac{\mathrm{Total} \mathrm{mass} \mathrm{of} 3 \mathrm{girls} \mathrm{and} 4 \mathrm{boys}}{7} = 35.2 \\ \Rightarrow \mathrm{Total} \mathrm{mass} \mathrm{of} 3 \mathrm{girls} \mathrm{and} 4 \mathrm{boys} = 246.4 \mathrm{kg} \\ \mathrm{Now}, \mathrm{mass} \mathrm{of} 4 \mathrm{boys} = 158.2 \mathrm{kg} \\ \mathrm{So}, \mathrm{mass} \mathrm{of} 3 \mathrm{girls} = 246.4 - 158.2 = 88.2 \mathrm{kg} \\ \mathrm{Now}, \mathrm{average} \mathrm{mass} \mathrm{of} 3 \mathrm{girls} = \frac{\mathrm{mass} \mathrm{of} 3 \mathrm{girls}}{3} = \frac{88.2}{3} = 29.4 \mathrm{kg} \end{gathered}$$

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