HOW MANY FOUR-DIGIT MULTIPLES OF 9 ARE THERE IF EACH OF...

3. How many four-digit multiples of 9 are there if each of the digits are odd and

distinct?

【Solution】

Since the sum of the four digits is also a multiple of 9, they must be 1, 3, 5 and 9. Any

of the 4!=24 permutations will yield a desired number.

ANS: 24