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 A1
but this includes two copies of each “triple” (R1)
number of ways of positioning “triplets” of science subjects A1
hence number of arrangements is M1A1
METHOD 2
consideration of all the non-science papers (M1)
hence all non-science papers can be sat in 15! ways A1
there are ways of positioning the three science papers (M1)A1
hence the number of arrangements is (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 M1A1
number of ways of positioning “triplets” of science subjects A1
hence number of arrangements is M1A1
[6 marks]