In a certain city, the charging standard for city calls is 0.2 yuan for the first 3 minutes, and 0.1 yuan for each additional minute (less than 1 minute is counted as 1 minute). Mom gives Dongdong 0.5 yuan to call grandma in this city. Can Dongdong and grandma chat for a few minutes?
某市的市话费收费标准是前3分钟0.2元，以后每增加1分钟(不足1分钟按1分钟计算)付0.1元．妈妈给冬冬0.5元，去打电话给本市的奶奶，冬冬和奶奶可以聊几分钟？
<gadget id="calculator">0.5 - 0.2</gadget>
<output>0.3</output>

<gadget id="calculator">0.3 / 0.1</gadget>
<output>3</output>

<gadget id="calculator">3 + 3 + 1</gadget>
<output>7</output>

<result>7</result>