The statistical department conducted a survey on the purchase of household electrical appliances by 39 households. They found that each household had at least one type of electrical appliance, including 25 households with radio tape recorders, 20 households with color TV sets, 12 households with refrigerators, 10 households with both tape recorders and color TV sets, and color TV sets. There are 3 households with refrigerators, there are no households with all three types of electrical appliances, and how many households have both radio cassette recorders and refrigerators.
统计部门对39户居民家用电器购买情况进行调查，他们发现每至少有一种电器，其中有收录机的25户，有彩电的20户，有冰箱的12户，收录机、彩电都有的10户，彩电、冰箱都有的3户，没有三种电器都具备的，收录机和电冰箱都有的共多少户．
<gadget id="calculator">25 - 10</gadget>
<output>15</output>

<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<gadget id="calculator">39 - 20</gadget>
<output>19</output>

<gadget id="calculator">9 - 19</gadget>
<output>-10</output>

<gadget id="calculator">15 + (-10)</gadget>
<output>5</output>

<result>5</result>