The 20 monkeys ate a total of 38 peaches. Each big monkey ate 3 peaches, and each small monkey ate 1 peach. Please calculate how many big monkeys there are.
20只猴子一共吃了38个桃，每只大猴吃3个，每只小猴吃1个，请你算一算，大猴有多少只．
<gadget id="calculator">20 * 1</gadget>
<output>20</output>

<gadget id="calculator">38 - 20</gadget>
<output>18</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<result>9</result>