There are three cards, one number is written on the front and the other side, the first one has 1 and 2, the second one has 3 and 4, the third one has 5 and 6 (the number 6 can't be seen as 9) ． Take two out of these three cards and put them in a row, so how many different two-digit numbers can be formed in total.
有三张卡片，正、反面各写有1个数字，第一张写有1和2，第二张写有3和4，第三张写有5和6(数字6不能倒过来看为9)．从这三张卡片中取出两张，放成一排，那么一共可以组成多少个不同的两位数．
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">6 * 4</gadget>
<output>24</output>

<result>24</result>