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DOTS Division
Take any pair of two digit numbers x=ab and y=cd where, without loss of generality, ab > cd . Form two 4 digit numbers r=abcd and s=cdab and calculate: {r^2 - s^2} /{x^2 - y^2}.
Sixational
The nth term of a sequence is given by the formula n^3 + 11n . Find the first four terms of the sequence given by this formula and the first term of the sequence which is bigger than one million. Prove that all terms of the sequence are divisible by 6.
Age 14 to 16
Challenge Level
My train left London between 6 a.m. and 7 a.m. and arrived in Paris between 9 a.m. and 10 a.m. I noticed that at the start and end of the journey the hands on my watch were in exactly the same positions but that the minute hand and hour hand had swapped places. What time exactly did the train leave London and how long did the journey take?
NRICH is part of the family of activities in the Millennium Mathematics Project.