Question

Regarding the arithmetic sequence **-6, -11/2, -5,...**, which of the following statements are correct? 1) The sum of the first 5 terms and the sum of the first 20 terms are equal. 2) The common difference is -1/2.

• A. Both 1 and 2 are correct
• B. 1 is correct and 2 is incorrect
• C. 1 is incorrect and 2 is correct
• D. Both 1 and 2 are incorrect

Answer 1

Answer:

B. 1 is correct and 2 is incorrect

Sum of first 5 terms = n/2(2a+(n-1)d) =5/2(-12+4×1/2) =-25 Sum of first 20 terms = 20/2{-12+19(1/2)} = 10{(-24+19)/2} = 5(-5) = 25 Common Difference= -11/2 - (-6) = 1/2