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Biscuit Decorations

Andrew decorated 20 biscuits to take to a party. He lined them up and put icing on every second biscuit and different decorations on other biscuits. How many biscuits weren't decorated?

Constant Counting

You can make a calculator count for you by any number you choose. You can count by ones to reach 24. You can count by twos to reach 24. What else can you count by to reach 24?

Number Detective

Follow the clues to find the mystery number.

Tables Teaser

Age 5 to 7 Challenge Level:

We had our first solution to NRICH sent in from Bhutan. Sonam at the Yurung Central School sent in this:


William and Jake from Boulcott School in New Zealand sent in solutions saying it took about 30 minutes.


Lauren from Westridge Private School for Girls in Pasadena, California sent in this explanation:

How I solved this problem is that I first use all the clues. How I used them is I used it for a column and a row and since there is few more, I filled other ones. Then I solved it. How I solved is that I used multiplication to get the correct number that is in the box. Then I used the other numbers to check my work.

Thank you for these solutions, of course you are still able to explore further since there are a number of different arrangements that may pop up!