Form the greatest six digit odd number and smallest six digit even number using the digits from 1 to 9 only once .What will be the sum of these numbers?

To form the greatest six-digit odd number, we can arrange the digits from 1 to 9 in descending order. The largest odd digit is 9, so it should be the leftmost digit. The remaining digits can be arranged in any order. Thus, the greatest six-digit odd number would be 9,876,543.

To form the smallest six-digit even number, we can arrange the digits from 1 to 9 in ascending order. Since we need an even number, the rightmost digit should be 2, as it is the smallest even digit. The remaining digits can be arranged in any order. Thus, the smallest six-digit even number would be 1,234,569.

Now, let's calculate the sum of these numbers:
9,876,543 + 1,234,569 = 11,111,112

Therefore, the sum of the greatest six-digit odd number and the smallest six-digit even number is 11,111,112.