#699. double digit subtraction w/ regrouping

Mathematics, level: all
Posted Thu Oct 15 10:25:19 PDT 2009 by Lisa Holder- O'Sullivan (Lisa Holder- O'Sullivan).
The End of Two and Three Digit Addition and Subtraction! The Tale of Place Value
LHES, Jupiter, FL
Materials Required: white boards or chalk boards
Activity Time: 30- 45mins
Concepts Taught: addition, subtraction, regrouping

Double digit subtraction lesson
Big Bottom Borrow!

Read story The End of Two and Three Digit Addition and Subtraction! The Tale of Place Value's Break Up get a copy at http://www.smashwords.com/books/view/4788 and review the part of the story that explains what each place value can hold (use tens block or drawings on the board to show this visually).

Next, put a simple two digit subtraction problem on the board (with out borrowing/ regrouping) then change the bottom ones digit to be larger than the top. Ask the students what the book said about a big number on the bottom...then say "I use the rhyme big bottom borrow" and explain you must borrow or regroup from the left to the right when there is not enough in the top to subtract from. Stand up and have the kids watch you, hit your waist with your right hand as you say "big bottom" move your left hand like pulling from left to right say "borrow". Then have the students stand up and repeat this phrase and actions.

Follow with modeling regrouping with double digit subtraction and have the students say if it is "big bottom", don't forget to talk through your problem to explain exactly what you are doing in the problem as you solve it.

Last, have the students work with partners to solve problems on the board on a white board. Tell the students to use math talk with their partner while they solve the problem. Review the problems they did with their partners whole group let students come up to the board to show process.