For finding, the sum of last ten terms, we write the given AP in reverse order i.e, 126, 124, 122,..., 12, 10, 8
Hence,first term (a) = 126, common difference, (d) = 124 - 126
So,
![S _{10} = \frac{10}{2} [ 2a + (10 - 1)d ] \:](https://tex.z-dn.net/?f=S%20_%7B10%7D%20%3D%20%5Cfrac%7B10%7D%7B2%7D%20%5B%202a%20%2B%20%2810%20-%201%29d%20%5D%20%5C%3A%20)
![= 5 [2(126) + 9( - 2) ]](https://tex.z-dn.net/?f=%20%3D%205%20%5B2%28126%29%20%2B%209%28%20-%202%29%20%5D%20)

Answer by JKismyhusbandbae: 8 × 4
Explanation/Work: There are 8 snack bags with 4 muffins in each. Multiply 8 × 4 to find the total number of muffins.
We know that
We can write an Arithmetic Sequence as a rule:
<span>an = a1 + d(n−1)</span>
where
<span>a1 = the first term
<span>d =the "common difference" between terms
in this problem
a1=15 a2=7 a3=-1 a4=-9 ..... an=-225
d=a2-a1
d=7-15-----> d=-8
</span></span>an = a1 + d(n−1)
for
an=-225
d=-8
a1=15
find n
-225=15+(-8)*(n-1)--> (n-1)=[-225-15]/-8----> n-1=30---> n=30+1---> n=31
the answer is31