Extinguishing 63834

During the fire extinguishing exercise, 40% of the foam was sprayed from the foam fire extinguisher. The entire device weighed 7 kg, and after training, it dropped to 4.6 kg. What was the weight of the empty device?

Correct answer:

m =  1 kg

Step-by-step explanation:

$$\begin{gathered} q=100\%-40\%=1-\frac{40}{100}=0.6 \\ m+p=7 \\ m+q\cdot p=4.6 \\ m+p=7 \\ m+0.6\cdot p=4.6 \\ m+p=7 \\ m+0.6p=4.6 \\ Row2-Row1\to Row2 \\ m+p=7 \\ -0.4p=-2.4 \\ p=\frac{-2.4}{-0.4}=6 \\ m=7-p=7-6=1=1\text{kg} \\ m=1 \\ p=6 \end{gathered}$$

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