BRITISH MATHEMATICAL OLYMPIAD                                         BRITISH MATHEMATICAL OLYMPIAD
Round 2 : Thursday, 16 February 1995
Time allowed Three and a half hours.
               Each question is worth 10 marks.
Instructions • Full written solutions - not just answers - are        1. Find all triples of positive integers (a, b, c) such that
               required, with complete proofs of any assertions                            ³     1 ´³     1 ´³      1´
               you may make. Marks awarded will depend on the                                1+       1+       1+       = 2.
                                                                                                 a        b         c
               clarity of your mathematical presentation. Work
               in rough first, and then draft your final version
               carefully before writing up your best attempt.
               Rough work should be handed in, but should be          2. Let ABC be a triangle, and D, E, F be the midpoints of
               clearly marked.                                           BC, CA, AB, respectively.
             • One or two complete solutions will gain far more          Prove that 6 DAC = 6 ABE if, and only if, 6 AF C = 6 ADB.
               credit than partial attempts at all four problems.
             • The use of rulers and compasses is allowed, but
               calculators and protractors are forbidden.             3. Let a, b, c be real numbers satisfying a < b < c, a + b + c = 6
             • Staple all the pages neatly together in the top left      and ab + bc + ca = 9.
               hand corner, with questions 1,2,3,4 in order, and
               the cover sheet at the front.                             Prove that 0 < a < 1 < b < 3 < c < 4.
                 In early March, twenty students will be invited      4. (a) Determine, with careful explanation, how many ways 2n
                 to attend the training session to be held at
                                                                             people can be paired off to form n teams of 2.
                 Trinity College, Cambridge (30 March – 2 April).
                 On the final morning of the training session,           (b) Prove that {(mn)!}2 is divisible by (m!)n+1 (n!)m+1 for all
                 students sit a paper with just 3 Olympiad-style             positive integers m, n.
                 problems. The UK Team - six members plus
                 one reserve - for this summer’s International
                 Mathematical Olympiad (to be held in Toronto,
                 Canada, 13–23 July) will be chosen immediately
                 thereafter.    Those selected will be expected
                 to participate in further correspondence work
                 between April and July, and to attend a
                 short residential session 2–6 July before leaving
                 for Canada.
                 Do not turn over until told to do so.