The ratio of potassium nitrate, sulfur and charcoal in the preparation of "black powder" in ancient China is 15:2:3. Now there are 50 kilograms of charcoal, and 1000 kilograms of "black powder" needs to be prepared, how many kilograms of charcoal are needed?
中国古代的"黑火药"配制中硝酸钾、硫磺、木炭的比例为15：2：3．今有木炭50千克，要配制"黑火药"1000千克，还需要木炭多少千克？
<gadget id="calculator">15 + 2 + 3</gadget>
<output>20</output>

<gadget id="calculator">3 / 20</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">1_000 * (3/20)</gadget>
<output>150</output>

<gadget id="calculator">150 - 50</gadget>
<output>100</output>

<result>100</result>