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Double Digit

Choose two digits and arrange them to make two double-digit numbers. Now add your double-digit numbers. Now add your single digit numbers. Divide your double-digit answer by your single-digit answer. Try lots of examples. What happens? Can you explain it?

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Repeaters

Choose any 3 digits and make a 6 digit number by repeating the 3 digits in the same order (e.g. 594594). Explain why whatever digits you choose the number will always be divisible by 7, 11 and 13.

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Digit Sum

What is the sum of all the digits in all the integers from one to one million?

More Mathematical Mysteries

Age 11 to 14 Challenge Level:

Write down a three-digit number

Three chickens.

Change the order of the digits to get a different number

Find the difference between the two three digit numbers

Add together the digits of your answer. If you arrive at a two-digit answer, add the two digits to reduce your answer to a single digit answer

Subtract $5$ from the number you have

Find that equivalent number letter in the alphabet (1=A, 2=B etc.)

Name a country that begins with letter

Anteater.

Using the second letter of the name of the country that you chose, name a jungle animal that starts with that letter.

Name the colour of that animal.

Using the final letter of the name of the country that you chose, name a different animal that starts with that letter.

Name a fruit that starts with the last letter of that animal's name.

Melon slice.

Did you end up with orange or apple?

How did I know?