The second term of a geometric series is 4 and the sum to infinity is 18.
Find the two possible values of rrr.
Find the corresponding two possible values of aaa.
Given that r r\,r takes the smaller of the two possible values, find the smallest value of n n\,n for which Sn>17.9S_n > 17.9Sn>17.9.
178 exam-style questions on Edexcel A Level Maths Sequences and Series, covering 3.1 Arithmetic Sequences, 3.2 Arithmetic Series, 3.3 Geometric Sequences, 3.4 Geometric Series, 3.5 Sum to Infinity, 3.6 Sigma Notation, 3.7 Recurrence Relations, and 3.8 Modelling with Series. Each one has a worked solution and a mark scheme showing where the marks go.