In today's math class, my son still didn't understand the trial and error method of division with divisor of two digits, so he went home to find his father. ? His father smiled and said, let me teach you a magic weapon to win.

This is the formula of commercial trial: lose one or two, and receive eight or nine. As a whole, the quotient of the "four institutes" is reduced by one, and the quotient of the "five advances" is increased by one. The same size is not divided by quotient 89, and the divisor is divided by half quotient 45. Don't forget to compare, the remainder must be small to remember.