Using any number among 1, 5, 9, and 13 as the numerator, and any number among 4, 8, 12, and 16 as the denominator, how many different true fractions can be formed?
用1、5、9、13中任意一个数作分子，4、8、12、16中任意一个数作分母，可组成多少个不同的真分数？
<result>10</result>