## 143. Math Puzzle $4 / 77$

A $1 \mathrm{~m} \times 2 \mathrm{~m}$ large sheet metal plate is to receive a $0.4 \mathrm{~mm}$ thick lacquer coating, with a 30 percent loss (including evaporation of the solvent) during spraying being taken into account. Due to a new suggestion, the loss is now only 20 percent.

How much lacquer is saved for the specified work as a result?
The volume of the dried coating is in liters: $V=1 \mathrm{~m} \cdot 2 \mathrm{~m} \cdot 0.4 \mathrm{~mm}=0.81$ For this, before the new proposal, the amount of paint $V_{1}$ required was such that: $0.7 V_{1}=0.81 ; V_{1}=$ 1.143 l

thereafter $V_{2}: 0.8 V_{2}=0.8 \mathrm{l} ; V_{2}=1 \mathrm{l}$

The benefit of the proposal resulted in a paint saving of $V_{1}-V_{2}=0.143$ l of paint for this plate. The benefit is of course much greater when several plates are painted, as is the case in modern mass production.