To determine if the sequence $13, 20, 27, 34, \dots$ is arithmetic, we need to check if there is a constant difference between consecutive terms.

Let's calculate the differences:

1. $20 - 13 = 7$
2. $27 - 20 = 7$
3. $34 - 27 = 7$

Since the difference between consecutive terms is consistently $7$, the sequence is arithmetic, and the common difference is $7$.

Thus, the correct answer is:

• a. yes; 7

Would you like more details or have any further questions?

Here are five related questions to expand on this topic:

1. What is the general formula for the nth term of an arithmetic sequence?
2. How can we find the sum of the first $n$ terms in an arithmetic sequence?
3. Can a sequence be geometric if the difference between terms is constant?
4. How would the sequence change if the common difference were negative?
5. What are some real-life examples of arithmetic sequences?

Tip: When analyzing sequences, always calculate the difference between consecutive terms to check if it's arithmetic.