A-LevelMathematicsSeries9709/12 · Oct/Nov 2022 · Q44 Marks
A geometric progression is such that the third term is 1764 and the sum of the second and third terms is 3444. Find the 50th term.
- A geometric progression is such that the third term is 1764 and the sum of the second and third terms is 3444. Find the 50th term.[4]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.
- B1 Two correct algebraic statements. ar² = 1764 and ar + ar² = 3444 or ar = 1680 or a(1-r³)/(1-r) = 3444
- M1 Any valid method, e.g. 1764 ÷ 1680 or from 20r² - 41r + 21 OE (condone solving using a calculator). Attempt to solve as far as r = or a =
- A1 Note: r = 1764 / (3444 - 1764) www implies B1 and M1. r = 1764/1680 or 21/20 or 1.05 [a = 1600]
- A1 AWRT e.g. 17 474.1..... 17 500
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