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The general formula of an arithmetic sequence is An = A1 + (n-1)d where An refers to the nth term, A1 refers to the first term d refers to the common difference Try using the above formula

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There are 20 data in total. Q1 should be (5th datum + 6th datum)/2 Q2 should be (10th datum + 11th datum)/2 Q3 should be (15th datum +16th datum)/2 Your own calculation is wrong. Calculate yourself again. (Ans: IQR=10)

Actually, all the answers given (a, b, c, d) are wrong. The correct answer should be e. CANNOT BE DETERMINED For a, an arithmetic sequence refers to a sequence that the difference between consecutive terms ((n+1)th term - nth term) is constant. Obviously 1-2 =/= 1/2-1 a is wrong Thus, c is wrong. For b, a geometric sequence refers to a sequence that the ratio between consecutive terms i.e. (n+1)th term/nth term is constant. Although the given four terms, such ratio is constant, i.e. 1/2=1/2/1=1/4 / 1/2, the fifth term is not given and you cannot know the general term of the sequence and thus the GENERAL ratio of the sequence. So, it CANNOT be determined if b is correct if the GENERAL TERM of the sequence is NOT GIVEN and so as d. Therefore, the answer is e, i.e. CANNOT BE DETERMINED. (Point to note: You can ONLY determine if a sequence is arithmetic or geometric by knowing its GENERAL TERM and test if the common difference or ratio is CONSTANT.