3. (10 points) Divide the nine natural numbers from 1 to 9 into two groups, such that the sum of the numbers in one group is 8 times the sum of the numbers in the other group. There are 

different ways to do this.
3
【Analysis】According to the problem, the sum of these two groups is the sum of numbers from 1 to 9, and then the sum of the smaller group can be found using the sum ratio formula, and then further solved.
【Solution】Solution: According to the problem, we have:
The sum of these two groups is: $1+2+3+\cdots+9=45$;
The sum of the smaller group is: $45 \div(8+1)=5$;
Among the numbers 1 to 9, the sums that equal 5 are $5, 1+4=5, 2+3=5$, for a total of 3 ways.
Answer: There are 3 different ways.
Therefore, the answer is: 3.