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?
Follow the clues to find the mystery number.
What do the digits in the number fifteen add up to? How many other
numbers have digits with the same total but no zeros?
Simply writing out the numbers $1 - 9$ along the top of your
paper can be a great help.
Imagine arranging your four two-digit numbers in columns to do
the addition sum, like this:
$5 \: 2$
$1 \; 9$
$5 \; 1$
$2 \; 9$
If the total has to be $100$, think about how the four digits
you choose could add to make the $0$ in the units column, then look
at the tens column.