Xiao Peng did quick calculation exercises, with 20 questions in each group, and the correct rate of the first three groups was 85%. Later he made another group, and the correct rate of four combinations reached 87.5%. How many questions did Xiao Peng get right in the last group?
肖鹏做速算练习，每组20道题，前三组的正确率为85%．后来他又做了一组，四组合起来的正确率达到87.5%．肖鹏最后一组作对了几道题？
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">87.5 / 100</gadget>
<output>0.875</output>

<gadget id="calculator">80 * 0.875</gadget>
<output>70</output>

<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<gadget id="calculator">85 / 100</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">60 * (17/20)</gadget>
<output>51</output>

<gadget id="calculator">70 - 51</gadget>
<output>19</output>

<result>19</result>