=5x1000-5+5+7x100-7+7+3x10-3+3 =5x999+5x1+7x99+7x1+3x9+3x1
=5000-5+5+700-7+7+30-3+3 =5(999+1)+7(99+1)+3(9+1)
=5000+700+30 =5x1000+7x100+3x10
=5730 =5000+700+30
=5730
巧算.5x999+5+99x7+7+3x9+3
=5x1000-5+5+7x100-7+7+3x10-3+3 =5x999+5x1+7x99+7x1+3x9+3x1
=5000-5+5+700-7+7+30-3+3 =5(999+1)+7(99+1)+3(9+1)
=5000+700+30 =5x1000+7x100+3x10
=5730 =5000+700+30
=5730