From the four numbers 2, 4, 5, and 10, how many true fractions of different sizes can be formed by taking two numerators and denominators each time as fractions.
从2、4、5、10这四个数中，每次取出两个作为分数的分子和分母，一共可以组成多少个大小不等的真分数．
<gadget id="calculator">1 + 2 + 3</gadget>
<output>6</output>

<gadget id="calculator">6 - 2</gadget>
<output>4</output>

<result>4</result>