78*102
=78*100+78*2
=7800+156
=7956
69*102
=69*100+69*2
=6900+138
=7038
12*98
=12*100-12*2
=1200-24
=117612*29+12101*38简便运算12*29+12=12*(29+1)=12*30=360101*38=100*38+1*38=380+38=418