You may also like

problem icon

Month Mania

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 icon

Spiders and Flies

There were 22 legs creeping across the web. How many flies? How many spiders?

problem icon

Claire's Counting Cards

Claire thinks she has the most sports cards in her album. "I have 12 pages with 2 cards on each page", says Claire. Ross counts his cards. "No! I have 3 cards on each of my pages and there are 8 pages in my album", he says. "I have most cards". Lucia looks in her album. "I only have six pages but there are four cards on every page. I think I have the most cards". Who is right?

What's Left?

Stage: 1 Challenge Level: Challenge Level:2 Challenge Level:2

Alistair from Histon and Impington Infants School says:

When I coloured all of the numbers that could be shared by 2, the even ones were coloured and the odd numbers were left. Then I coloured all the numbers that could be shared by 3. When I tried the numbers that could be shared by 4, there were no new ones because they were even. When I tried the numbers that could be shared by 5, I found they were already coloured.

Alistair sent us a diagram of his results:

numbers 1-20 with 1, 2, 3, 5, 7, 11, 13, 17, and 19 left unshaded

Sim who lives in Singapore explains that the (black) numbers left are 7, 11, 13, 17, and 19, and that they are called prime numbers. Well done.

Sim also points out that 2, 3 and 5 are prime numbers too. I wonder whether anyone can notice something different about 2, the lowest prime number, compared with the others?