If two boards each 1 meter long are nailed to a length of 170 cm, how long is the place where they are nailed together in the middle?
把两块各有1米长的木板钉成了一条长170厘米，中间钉在一起的地方有多长？
<gadget id="calculator">1 * 100 * 2</gadget>
<output>200</output>

<gadget id="calculator">200 - 170</gadget>
<output>30</output>

<result>30</result>