In a group of tourists, 75% understand French, 80% understand English, 65% understand both languages, and another 10 people do not understand both languages. How many tourists are there in this group?
在一批游客中，有75%的人懂法语，80%的人懂英语，两种语言都懂的占65%，另有10人这两种语言都不懂，这批游客有多少人？
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">65 / 100</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">(4/5) - (13/20)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(3/4) + (3/20)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">10 / (1/10)</gadget>
<output>100</output>

<result>100</result>