Final answer:
To find s20, the sum of the first 20 terms of an arithmetic series given a1=855 and a20=760, use the formula Sn = n/2 * (a1 + an). The calculated sum is 16150, which is not among the provided options. There might be a typo in the question.
Step-by-step explanation:
To find the sum of the first 20 terms (s20) of an arithmetic series when the first term (a1) is 855 and the 20th term (a20) is 760, we can use the formula for the sum of an arithmetic series:
Sn = n/2 (a1 + an)
Substituting the given values, we have:
S20 = 20/2 (855 + 760)
S20 = 10 (1615)
S20 = 16150
Therefore, the sum of the first 20 terms of the arithmetic series is 16150, which does not match any of the options provided. If there is a typo in the question and the options are incorrect, we would reconsider the answer based on the correct options. If the student has provided the correct options, then the provided options are all incorrect based on the calculation.