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Date May 2017 Marks available 6 Reference code 17M.2.AHL.TZ2.H_8
Level Additional Higher Level Paper Paper 2 Time zone Time zone 2
Command term Find Question number H_8 Adapted from N/A

Question

In a trial examination session a candidate at a school has to take 18 examination papers including the physics paper, the chemistry paper and the biology paper. No two of these three papers may be taken consecutively. There is no restriction on the order in which the other examination papers may be taken.

Find the number of different orders in which these 18 examination papers may be taken.

Markscheme

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

METHOD 1

consideration of all papers

all papers may be sat in 18! ways     A1

number of ways of positioning “pairs” of science subjects = 3 ! × 17 !      A1

but this includes two copies of each “triple”     (R1)

number of ways of positioning “triplets” of science subjects = 3 ! × 16 !      A1

hence number of arrangements is 18 ! 3 ! × 17 ! + 3 ! × 16 !      M1A1

( = 4.39 × 10 15 )

METHOD 2

consideration of all the non-science papers     (M1)

hence all non-science papers can be sat in 15! ways     A1

there are 16 × 15 × 14   ( = 3360 ) ways of positioning the three science papers     (M1)A1

hence the number of arrangements is 16 × 15 × 14 × 15 !  ( = 4.39 × 10 15 )      (M1)A1

METHOD 3

consideration of all papers

all papers may be sat in 18! ways     A1

number of ways of positioning exactly two science subjects = 3 ! × 15 ! × 16 × 15      M1A1

number of ways of positioning “triplets” of science subjects = 3 ! × 16 !      A1

hence number of arrangements is 18 ! 3 ! × 16 ! 3 ! × 15 ! × 16 × 15      M1A1

( = 4.39 × 10 15 )

[6 marks]

Examiners report

[N/A]

Syllabus sections

Topic 1—Number and algebra » SL 1.9—Binomial theorem where n is an integer
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