Answer: -1/9
Step by step explanation:
The common difference of an arithmetic sequence can be found by picking 2 consecutive terms, and subtracting the second from the first. For example, if I chose the terms 2 and 1 8/9, I would find the common difference by:
1 8/9 - 2, which is equal to -1/9.
You can confirm this by picking another pair of consecutive terms. Let's pick 1 7/9 and 1 2/3:
1 2/3 - 1 7/9 = -1/9, as 1 2/3 = 1 6/9, so 1 6/9 - 1 7/9 = -1/9