Addition and subtraction

problem
Sometimes we lose things

Age

7 to 11

Challenge level

Well now, what would happen if we lost all the nines in our number system? Have a go at writing the numbers out in this way and have a look at the multiplications table.
problem
Doplication

Age

7 to 11

Challenge level

We can arrange dots in a similar way to the 5 on a dice and they usually sit quite well into a rectangular shape. How many altogether in this 3 by 5? What happens for other sizes?
problem
Month mania

Age

5 to 11

Challenge level

Can you design a new shape for the twenty-eight squares and arrange the numbers in a logical way? What patterns do you notice?
problem
Dice and spinner numbers

Age

7 to 11

Challenge level

If you had any number of ordinary dice, what are the possible ways of making their totals 6? What would the product of the dice be each time?
problem
Sending cards

Age

7 to 11

Challenge level

This challenge asks you to investigate the total number of cards that would be sent if four children send one to all three others. How many would be sent if there were five children? Six?
problem
I'm eight

Age

5 to 11

Challenge level

Find a great variety of ways of asking questions which make 8.
problem
Roll these dice

Age

7 to 11

Challenge level

Roll two red dice and a green dice. Add the two numbers on the red dice and take away the number on the green. What are all the different possible answers?
problem
Times

Age

7 to 11

Challenge level

Which times on a digital clock have a line of symmetry? Which look the same upside-down? You might like to try this investigation and find out!
problem
Number squares

Age

5 to 11

Challenge level

Start with four numbers at the corners of a square and put the total of two corners in the middle of that side. Keep going... Can you estimate what the size of the last four numbers will be?
problem
Worms

Age

7 to 11

Challenge level

Place this "worm" on the 100 square and find the total of the four squares it covers. Keeping its head in the same place, what other totals can you make?