A geometric progression has first term $216$ and fourth term $64$.
(a)[3]
Calculate the sum to infinity of the progression.
(b)[6]
The second term of the geometric progression matches the second term of an arithmetic progression. The third term of the geometric progression matches the fifth term of the same arithmetic progression. Find the sum of the first $21$ terms of the arithmetic progression.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Determines the common ratio as $r=\frac{2}{3}$” …