## Task 1 - 020831

Zinc blende is an ore and contains 65 percent zinc. Of this zinc content, 15 percent is lost during extraction.

How many kg of zinc blende are required to obtain $1000 \mathrm{~kg}$ of zinc?
The $1000 \mathrm{~kg}$ of zinc to be obtained is $85 \%$ of the zinc contained in the sphalerite, so $100 \%$ is $1176.5 \mathrm{~kg}$. This in turn is $65 \%$ of the total amount of sphalerite, which must therefore be 1810 $\mathrm{kg}$.