数学题求救，先谢了

来源: 于 2012-04-12 07:10:10 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

how many 7-digit numbers in base 10 are possible

1. if one digit occurs exactly four times, and there are no other repeats?

2. if two digits each occur exactly twice, and there aer no other repeats?

谢谢了。