ex 8 )
489200 .......490000
900770........900000
699900........700000
912770........910000
679900........680000
ex 9)
538 , 558, 578, 598, 618, 638
ex 10)
a................200.
b....................5
a * b..........1000.
a : b.............40
a - b ...........195
a + b ..........205
