Jack does a 20-question quiz. How many questions didn't he attempt?

Gar the Magician plays a card trick on his friends Kan and Roo. Can you work out his trick and find out the sum on Kan's cards?

The sum of each column and row in this grid give the totals as shown. What number goes in the starred square?

From only the page numbers on one sheet of newspaper, can you work out how many sheets there are altogether?

Find a number between 100 and 999 that has its middle digit equal to the sum of the other two digits. Can you find all possibilities?

Repeat a pattern of numbers to form a larger number. Can you find the sum of all the digits?

What is the largest number of digits that could be erased from this 1000-digit number, to get a surprising result?

Alberta won't reveal her age. Can you work it out from these clues?

Can you find a number and its double using the digits $1$ to $9$ only once each?