1. Can the numbers in an arithmetic sequence go down?
Yes, if the common difference is negative the terms will decrease.
2. Do you HAVE to take the first term away from the second term to find the common difference?
No, this will work, but you can subtract ANY term from the one after it to find the common difference.
3. Does the common difference have to be the same between every pair of terms for a sequence to be an arithmetic sequence?
4. How are arithmetic sequences used in real life?
Anywhere there is a pattern there is probably a sequence of some sort.
e.g. Laying tiles or paving stones or depositing a fixed amount of money each week into a bank account could form arithmetic sequences.