Think of a two digit number, say 42, then
subtract the reverse of its digits, 24, from 42
42-24 =18
hence 18 is product of 9
also 1+8=9
Choose any two digits number
and for each one reverse the digits and subtract the smaller number from the
larger. Look at all the answers you get. Do they all have
a common divisor? What do the digits sum to each time?
Some
Examples:
92-29 =63
hence 63 is product of 9
also 6+3=9
41-14 =27
hence 27 is product of 9
also 2+7 =9
83-38 =45
hence 45 is product of 9
also 4+5 =9
You see how fascinating and enjoying it is. In
each case the difference is divisible by 9 (i.e. the common factor is 9) and
the sum of the digits of the difference is always 9.