Among the four numbers 1, 3, 7, and 9, three numbers are randomly selected to form a three-digit number, how many different three-digit numbers can be formed in total.
在1、3、7、9四个数字中，任意选出三个数字组成三位数，一共可以组成多少个不同的三位数．
<gadget id="calculator">4 * 3 * 2</gadget>
<output>24</output>

<result>24</result>