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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 rr.

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=u11r33.25=u11r

correct substitution into formula for unun (seen anywhere)      (A1)

eg     7.98=u1r7.98=u1r

attempt to express u1u1 in terms of rr (or vice-versa)      (M1)

eg     u1=7.98ru1=7.98r,   u1=33.25(1r)u1=33.25(1r),   r=7.98u1r=7.98u1,   r=33.25u133.25r=33.25u133.25

correct working      (A1)

eg    (7.98r)1r=33.25(7.98r)1r=33.25,   33.25(1r)=7.98r33.25(1r)=7.98r,   (0.4, 19.95),   (0.6, 13.3),   u117.98u1=33.25u117.98u1=33.25

r=0.4(=25)r=0.4(=25)r=0.6(=35)r=0.6(=35)        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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