Reasoning, convincing and proving

There are 514 NRICH Mathematical resources connected to Reasoning, convincing and proving
Rhombus in Rectangle
problem

Rhombus in rectangle

Age
14 to 16
Challenge level
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Take any rectangle ABCD such that AB > BC. The point P is on AB and Q is on CD. Show that there is exactly one position of P and Q such that APCQ is a rhombus.
The Genie in the Jar
problem

The genie in the jar

Age
11 to 14
Challenge level
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This jar used to hold perfumed oil. It contained enough oil to fill granid silver bottles. Each bottle held enough to fill ozvik golden goblets and each goblet held enough to fill vaswik crystal spoons. Each day a spoonful was used to perfume the bath of a beautiful princess. For how many days did the whole jar last? The genie's master replied: Five hundred and ninety five days. What three numbers do the genie's words granid, ozvik and vaswik stand for?
Clocked
problem

Clocked

Age
11 to 14
Challenge level
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Is it possible to rearrange the numbers 1,2......12 around a clock face in such a way that every two numbers in adjacent positions differ by any of 3, 4 or 5 hours?
Golden Eggs
problem

Golden eggs

Age
16 to 18
Challenge level
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Find a connection between the shape of a special ellipse and an infinite string of nested square roots.
Trig Rules OK
problem

Trig rules ok

Age
16 to 18
Challenge level
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Change the squares in this diagram and spot the property that stays the same for the triangles. Explain...
So Many Sums
problem

So many sums

Age
11 to 14
Challenge level
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In this addition each letter stands for a different digit, with S standing for 3. What is the value of YxO?
Road maker 2
problem

Road maker 2

Age
16 to 18
Challenge level
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Can you work out where the blue-and-red brick roads end?
Geometric Parabola
problem

Geometric parabola

Age
14 to 16
Challenge level
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Explore what happens when you draw graphs of quadratic equations with coefficients based on a geometric sequence.
Fixing It
problem

Fixing it

Age
16 to 18
Challenge level
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A and B are two fixed points on a circle and RS is a variable diamater. What is the locus of the intersection P of AR and BS?
Stonehenge
problem

Stonehenge

Age
16 to 18
Challenge level
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Explain why, when moving heavy objects on rollers, the object moves twice as fast as the rollers. Try a similar experiment yourself.