3. The number 916238457 is an example of a nine-digit number which
try all the problems.
contains each of the digits 1 to 9 exactly once. It also has the property
that the digits 1 to 5 occur in their natural order, while the digits 1
• Each question carries 10 marks. However, earlier
to 6 do not. How many such numbers are there?
questions tend to be easier. In general you are
advised to concentrate on these problems first.
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