There are 4 numbers in a set of data, and the mean, mode and median of these 4 numbers are all 60. Where the largest number is 90, what is the smallest number?
一组数据共有4个数，这4个数的平均数、众数和中位数都是60．其中最大的数是90，最小的数是多少．
<gadget id="calculator">60 * 4</gadget>
<output>240</output>

<gadget id="calculator">60 * 2</gadget>
<output>120</output>

<gadget id="calculator">240 - 90 - 120</gadget>
<output>30</output>

<result>30</result>