Moderate -0.8 This is a straightforward application of the sum to infinity formula S_∞ = a/(1-r). Given a=8 and S_∞=10, students simply substitute and solve 10 = 8/(1-r) to find r=0.2. It requires only recall of a single formula and basic algebraic manipulation, making it easier than average but not trivial since it involves the sum to infinity concept.
5 The first term of a geometric series is 8. The sum to infinity of the series is 10 .\\
Find the common ratio.
\hfill \mbox{\textit{OCR MEI C2 Q5 [3]}}