Answer:
The sum of the first 20 terms is 2450
Step-by-step explanation:
Sum of nth terms of an arithmetic sequence is
Sn = n/2 [2a+ (n -1)d]
Therefore, the sum of the first 20 terms
where first term = a = 18 and common difference = d = 11 is
S_20 = 20/2 [2(18) + (20 -1)11]
S_20 = 10 [36 + (19)11]
S_20 = 10 [36 + 209]
S_20 = 10 [245]
S_20 = 2450
