class held a parent-teacher meeting, and prepared a teacup for each parent, but there were 5 missing; and half of the original cups were borrowed, but there were 13 more cups. How many parents are there this time?
一个班召开家长会，给每一个家长备一只茶杯，结果少5只；又借来原来的杯子数的一半，这时却多出了13只杯子．这次到会的家长有多少人．
<gadget id="calculator">5 + 13</gadget>
<output>18</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) - 1</gadget>
<output>-1/2 = around -0.5</output>

<gadget id="calculator">1 + (-1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">18 / (1/2)</gadget>
<output>36</output>

<gadget id="calculator">36 + 5</gadget>
<output>41</output>

<result>41</result>