There are 20 girls in the third grade, and 12 boys are twice as many as girls. How many boys are there?
三年级有女生20人，男生比女生的2倍少12人，男生有多少人．
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">40 - 12</gadget>
<output>28</output>

<result>28</result>