34. Using each of the nine digits $1,2,3, \ldots, 9$ exactly once, write down three numbers such that their sum is the greatest possible, and the difference between the largest and smallest numbers is as small as possible. Find this sum and difference.
34. To make the sum the largest, the hundreds should be 9, 8, and 7, the tens should be 6, 5, 4, and the units should be 3, 2, and 1. The larger number has 9 hundreds, and the smaller one has 7. To make their difference the smallest, the larger number should have as few tens and units as possible, while the smaller number should have as many as possible. Therefore, the larger number is 941, and the smaller one is 763. Then the third number is 852. We have $941+852+763=2556, 941-763=178$.