1.)Read Shark Swimathon by Stuart J. Murphy. (Overview: The Ocean City Sharks have to swim 75 laps by the end of the week, and every day they figure out how many laps are left to go. Swimming and subtraction are all part of the fun!)
During the reading, pause and instruct students to compute the math problems from the book on dry erase boards or paper. Another option is to have half of the students use calculators to compute the problems, if this is a skill that has been introduced previously, and compare answers at the end of the book. (This is a twodigit subtraction book that will review skills prior to the introduction of threedigit subtraction.)
2.)Give a number description orally and instruct students to write the threedigit number described on their dry erase boards or paper. Example: What number has 6 hundreds, no tens, and no ones? (600) Brainstorm other ways to depict the same number. Example: 5 hundreds, 10 tens and no ones OR 4 hundreds, 10 tens and 100 ones, etc.
3.)Using base ten blocks (unifix cubes) made for overhead projectors, model the subtraction of 175 from 600. An alternaive is to use the following link to an interactive site that uses base ten blocks to depict subtraction problems. Regardless of the method chosen, model regrouping across zeros. Complete several practice problems, then have students work in small groups with manipulatives to solve threedigit subtraction problems. Allow individual practice either at the overhead or on the website. ( Virtual Manipulative: Base Block Subtraction) Click on "Create a Problem".
4.)After adequate practice with the base ten blocks students will practice computing threedigit subtraction problems. Roll three dice to arrive at a threedigit number. Record the number. Roll the dice again to arrive at a second threedigit number. Students should determine which number is larger and create a subtraction problem using the two numbers. Students will compute the problem on dry erase boards and reveal their work to the teacher. A nod or thumbs up can be given to students with correct answers. Depending on time students can play the dice game in small groups. ( Welcome to WebDice!) This site may be used it you are short on dice.
6.)As a cummulative project assign groups of students to work together to write a story similar to Shark Swimathon that involves threedigit math problems as part of the story. As an alternative write a story as a large group. Use desktop publishing/word processing software to create a finished product. Books can then become a part of the classroom math library.
