What do the digits in the number fifteen add up to? How many other
numbers have digits with the same total but no zeros?
A church hymn book contains 700 hymns. The numbers of the hymns are
displayed by combining special small single-digit boards. What is
the minimum number of small boards that is needed?
In the multiplication sum, some of the digits have been replaced by letters and others by asterisks. Can you reconstruct the original multiplication?
An obvious extension is for the children to make up their own
examples for each other. They could repeat the format of the given
problem, or play 'what's my number?' with a partner, where they try
to find out what the mystery number is in the minimum number of
guesses. Give an opportunity for them to describe why some
questions are more useful than others.