27) 38=30+8 ,66=32+34...etc
28) 45=54;62=26;75=57;89=98;54=45;
29) 15,24,42,51.........18,27,36,45,54,63,72,81..........14,23,32,41.
30) 18,28,38.......98
50,51,52,.......59
90,91,92.......99.
31) a) 94,83,72,61,50
b)93,82,71,60
32) 2034,2340,2403,2304 ,3420,3204,3042,3024,4302,4203,4032,4023