The question asks, "Which of the following is an arithmetic sequence?" Let's analyze each option:

1. $-20, -25, -30, -35, -45, \dots$:
   To check if it's an arithmetic sequence, find the difference between consecutive terms:

   • $-25 - (-20) = -5$
   • $-30 - (-25) = -5$
   • $-35 - (-30) = -5$
   • $-45 - (-35) = -10$

   The difference is not consistent (changes from $-5$ to $-10$), so it's not an arithmetic sequence.

2. $-15.6, -12.9, -10.2, -7.5, -4.8, \dots$:
   Check the differences:

   • $-12.9 - (-15.6) = 2.7$
   • $-10.2 - (-12.9) = 2.7$
   • $-7.5 - (-10.2) = 2.7$
   • $-4.8 - (-7.5) = 2.7$

   The difference is consistent, so this is an arithmetic sequence.

3. $3.1, 6.2, 12.4, 24.8, 49.6, \dots$:
   Check the ratios (this might suggest a geometric sequence):

   • $6.2 / 3.1 = 2$
   • $12.4 / 6.2 = 2$
   • $24.8 / 12.4 = 2$

   This sequence follows a geometric progression, so it's not an arithmetic sequence.

4. $7.2, 3.6, 1.8, 0.9, 0.45, \dots$:
   Check the ratios:

   • $3.6 / 7.2 = 0.5$
   • $1.8 / 3.6 = 0.5$
   • $0.9 / 1.8 = 0.5$

   This is another geometric sequence, so it's not an arithmetic sequence.

Correct Answer:

The arithmetic sequence is $-15.6, -12.9, -10.2, -7.5, -4.8, \dots$.

Would you like a breakdown of arithmetic sequences or help with another topic?

1. What is the formula for the $n$-th term of an arithmetic sequence?
2. How can we distinguish between arithmetic and geometric sequences?
3. What are some real-life applications of arithmetic sequences?
4. How do you find the sum of the first $n$ terms of an arithmetic sequence?
5. Can a sequence be both arithmetic and geometric?

Tip: Always check the consistency of differences between terms to identify an arithmetic sequence.