Answer: 132
Step-by-step explanation
The formula I'll use is
Sn = (n/2)*(2*a1 + d*(n-1))
the variables are
- n = number of terms
- a1 = first term
- d = common difference
- Sn = sum of the first n terms
In this case we have these values
- n = 22
- a1 = 153
- d = -14 since we go down by 14 each time
So,
Sn = (n/2)*(2*a1 + d*(n-1))
S22 = (22/2)*(2*153 + (-14)*(22-1))
S22 = 132
The first 22 terms of the arithmetic sequence 153, 139, 125, ... sum to 132