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1.4 Sequences and Series

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Question 26

A geometric sequence has first term aaa and common ratio rrr, where r>0r > 0r>0.

Given that

  • the 2nd term is 12
  • the 4th term is 6.75
a.

Show that r=0.75r = 0.75r=0.75.

[2]
b.

Hence find the value of aaa.

[1]
c.

Given that the sum of the first nnn terms of this sequence is greater than 63.5

Find the smallest possible value of nnn.

(Solutions based entirely on graphical or numerical methods are not acceptable.)

[5]
Markscheme

1.4 Sequences and Series Questions

  1. A Level
  2. /Maths
  3. /1.4 Sequences and Series

308 exam-style questions on OCR A Level Maths 1.4 Sequences and Series, covering 1.4.1 Binomial expansion for positive integer n, 1.4.2 Link to binomial probabilities, 1.4.3 Binomial expansion for rational n (A-level only), 1.4.4 Validity of the expansion (A-level only), 1.4.5 Sequences (A-level only), 1.4.6 Increasing, decreasing and periodic sequences (A-level only), 1.4.7 Sigma notation (A-level only), 1.4.8 Arithmetic sequences and series (A-level only), 1.4.9 Geometric sequences and series (A-level only), 1.4.10 Sum to infinity of a geometric series (A-level only), and 1.4.11 Modelling with sequences and series (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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