Question 1 In an arithmetic series, the 18th term is 139 and the 7th term is 51 a) What is the common difference? Expected answer: Save answer Score: 0/1 Feedback for a). Show feedback.The feedback has changed.This feedback is based on your last submitted answer. Save your changed answer to get updated feedback. Or, you could: ⤺ Go back to the previous part There's nothing more to do from here.b) Determine the least positive value for n for which the sum of the first n terms of the series exceeds 1000.Expected answer: Save answer Score: 0/1 Feedback for b). Show feedback.The feedback has changed.This feedback is based on your last submitted answer. Save your changed answer to get updated feedback. Or, you could: ⤺ Go back to the previous part There's nothing more to do from here. Advice To find the common difference d we note that the 18th term is 139 and the 7th term is 51 so we can find the common difference d by noting 51−139=(7−18)×d, hence common difference =8 To find the least positive value for n for which the sum of the first n terms of the series exceeds 1000, we recall that the sum of an arithmetic series can be found with the formula Sn=n(2a1+(n−1)×d)2 where a1 denotes the first term and d denotes the common difference. Now we want to find the smallest positive n such that Sn>1000. This is now a matter of solving a quadratic, which is left as an exercise. Score: 0/2 Total 0/2 Move to the next questionTry another question like this oneReveal answers