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Date November 2018 Marks available 6 Reference code 18N.2.SL.TZ0.S_5
Level Standard Level Paper Paper 2 Time zone Time zone 0
Command term Find Question number S_5 Adapted from N/A

Question

The sum of an infinite geometric sequence is 33.25. The second term of the sequence is 7.98. Find the possible values of r .

Markscheme

* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.

correct substitution into formula for infinite geometric series      (A1)

eg      33.25 = u 1 1 r

correct substitution into formula for u n (seen anywhere)      (A1)

eg      7.98 = u 1 r

attempt to express u 1 in terms of r (or vice-versa)      (M1)

eg      u 1 = 7.98 r ,    u 1 = 33.25 ( 1 r ) ,    r = 7.98 u 1 ,    r = 33.25 u 1 33.25

correct working      (A1)

eg    ( 7.98 r ) 1 r = 33.25 ,    33.25 ( 1 r ) = 7.98 r ,   (0.4, 19.95),   (0.6, 13.3),    u 1 1 7.98 u 1 = 33.25

r = 0.4 ( = 2 5 ) r = 0.6 ( = 3 5 )         A1A1 N3

 

[6 marks]

Examiners report

[N/A]

Syllabus sections

Topic 1—Number and algebra » SL 1.2—Arithmetic sequences and series
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Topic 1—Number and algebra

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