Using 2, 3, 7, 9 to form a two-digit number without repeating numbers, how many two-digit numbers can be formed with an odd number.
用2、3、7、9组成没有重复数字的两位数，能组成多少个个位是单数的两位数．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<result>9</result>