A geometric progression has first term a and common ratio r, where r > 0. The sum of the 2nd and 3rd terms of the progression is 168. The sum of the 4th and 5th terms of the progression is 94.5.
- (a)Find the 6th term of the progression.[7]
- (b)Find the sum to infinity of the progression.[1]
Mark scheme
Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.
- [B1] ar + ar² = 168 or ar³ + ar⁴ = 94.5 oe soi
- [M1] Correct equation where a can be directly eliminated ar³(1+r) / ar(1+r) = 94.5 / 168 oe
- [M1] 168r² = 94.5 oe
- [A1] r = 3/4 only nfww
- [M1] FT their r -a - a(3/4) = 168 oe
- [A1] a = 128
- [B1] u₆ = 243/8 only oe, isw
- [B1] 512
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