How many terms are in the arithmetic sequence 5, 1, −3, . . . , −111? Hint: an = a1 + d(n − 1), where a1 is the first term and d is the common difference.
5+(n-1)(4)=-111, (n-1)(4)=-116, n-1=-29, so n=30, 30 terms.
[L - F] / D + 1 = N, where L=Last term, F =First term, D=Common difference, N =Number of terms.
[-111 - 5] / - 4 + 1 = N
[-116] / -4 + 1 = N
29 + 1 = N
N = 30 - Number of terms.
