Odd and even numbers

There are 75 NRICH Mathematical resources connected to Odd and even numbers
Arrangements
problem

Arrangements

Age
7 to 11
Challenge level
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Is it possible to place 2 counters on the 3 by 3 grid so that there is an even number of counters in every row and every column? How about if you have 3 counters or 4 counters or....?
Jenny's Logic
problem

Jenny's logic

Age
11 to 14
Challenge level
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Weekly Problem 52 - 2009
How did Jenny figure out that Tom's cards added to an even number?
Great Granddad
problem

Great granddad

Age
11 to 14
Challenge level
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Great Granddad is very proud of his telegram from the Queen congratulating him on his hundredth birthday and he has friends who are even older than he is... When was he born?
FEMTO
game

Femto

A new card game for two players.

Prime Magic
problem

Prime magic

Age
7 to 16
Challenge level
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Place the numbers 1, 2, 3,..., 9 one on each square of a 3 by 3 grid so that all the rows and columns add up to a prime number. How many different solutions can you find?
Diagonal Trace
problem

Diagonal trace

Age
7 to 11
Challenge level
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You can trace over all of the diagonals of a pentagon without lifting your pencil and without going over any more than once. Can the same thing be done with a hexagon or with a heptagon?
Odds and Threes
game

Odds and threes

A game for 2 people using a pack of cards Turn over 2 cards and try to make an odd number or a multiple of 3.

What number?
problem

What number?

Age
5 to 7
Challenge level
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I am less than 25. My ones digit is twice my tens digit. My digits add up to an even number.
Crossings
problem

Crossings

Age
7 to 11
Challenge level
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In this problem we are looking at sets of parallel sticks that cross each other. What is the least number of crossings you can make? And the greatest?