Master Wang saw a 20-meter-long aluminum alloy window into 5 sections. If the loss of the aluminum alloy is 3mm every time you saw it, how long will the aluminum alloy be after sawing?
王师傅一扇门铝合金的窗户，把一根长20米的铝合金锯成5段，如果每锯一次铝合金的损耗是3毫米，锯完后这根铝合金还有多长？
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">4 / 1_000</gadget>
<output>1/250 = around 0.004</output>

<gadget id="calculator">3 * (1/250)</gadget>
<output>3/250 = around 0.012</output>

<gadget id="calculator">20 - (3/250)</gadget>
<output>4_997/250 = around 19.988</output>

<result>4_997/250 = around 19.988</result>