Reasoning, convincing and proving

There are 458 NRICH Mathematical resources connected to Reasoning, convincing and proving
Football crazy Hockey mad
problem

Football crazy Hockey mad

Age
11 to 14
Challenge level
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In a league of 5 football teams which play in a round robin tournament show that it is possible for all five teams to be league leaders.
Flight of the Flibbins
problem

Flight of the Flibbins

Age
11 to 14
Challenge level
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Blue Flibbins are so jealous of their red partners that they will not leave them on their own with any other bue Flibbin. What is the quickest way of getting the five pairs of Flibbins safely to the new planet?
Pattern of islands
problem

Pattern of islands

Age
11 to 14
Challenge level
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In how many distinct ways can six islands be joined by bridges so that each island can be reached from every other island...
Dicing with numbers
problem

Dicing with numbers

Age
11 to 14
Challenge level
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In how many ways can you arrange three dice side by side on a surface so that the sum of the numbers on each of the four faces (top, bottom, front and back) is equal?
Not necessarily in that order
problem

Not necessarily in that order

Age
11 to 14
Challenge level
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Baker, Cooper, Jones and Smith are four people whose occupations are teacher, welder, mechanic and programmer, but not necessarily in that order. What is each person’s occupation?
Master Minding
problem

Master Minding

Age
11 to 14
Challenge level
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Your partner chooses two beads and places them side by side behind a screen. What is the minimum number of guesses you would need to be sure of guessing the two beads and their positions?
Marbles in a box
problem

Marbles in a box

Age
11 to 16
Challenge level
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How many winning lines can you make in a three-dimensional version of noughts and crosses?
Number rules - OK
problem

Number rules - OK

Age
14 to 16
Challenge level
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Can you produce convincing arguments that a selection of statements about numbers are true?
Parallel Universe
problem

Parallel Universe

Age
14 to 16
Challenge level
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An equilateral triangle is constructed on BC. A line QD is drawn, where Q is the midpoint of AC. Prove that AB // QD.
Square Pair Circles
problem

Square Pair Circles

Age
16 to 18
Challenge level
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Investigate the number of points with integer coordinates on circles with centres at the origin for which the square of the radius is a power of 5.