Beacon Lesson Plan Library
Mary Ann Taylor
Bay District Schools
Students will subtract two-digit numbers and use addition to check their subtraction.
The student understands and explains the effects of addition, subtraction, and multiplication on whole numbers, decimals, and fractions, including mixed numbers, and the effects of division on whole numbers, including the inverse relationship of multiplication and division.
The student explains and demonstrates the addition and subtraction of whole numbers (up to three digits or more) using concrete materials, drawings, symbols, and algorithms.
-Teacher made subtraction cards (Can be made with index cards or cardstock)
1. Make 40 or more cards with different subtraction problems on them. Some should be with regrouping and some should not. They can be made from index cards or cardstock.
1. Write 54-23 vertically on the chalkboard. Have a volunteer go to the chalkboard to write the answer. Have the student explain each step as he/she does it. Ex: First you subtract 3 ones from 4 ones. You write the answer 1 in the ones column. Then you subtract the 2 tens from 5 tens. You write 3 in the tens column. The difference is 31. Ask the student how he/she can check their answer to make sure it is correct. (Check it with addition.) Then have the student check the answer with addition on the chalkboard. Have the student explain each step as he/she does it.
2. Repeat step 1 with another subtraction problem that requires regrouping. Have volunteers work out 2 more that need regrouping and 2 more that donít need regrouping. (Some prior knowledge of subtracting two digit numbers with and without regrouping and checking subtraction with addition should be known to complete this activity.)
3. Pass out paper and pencils to each student.
4. Tell the class that they are going to play subtraction relay.
5. Divide the class into two groups. Tell the students that you have cards with subtraction problems on them for each group. To play the game, a student from each group will pick a card and write the subtraction problem on the chalkboard. All the students on each team will copy the problem their teammate wrote on the board onto their paper. While the students at the chalkboard work out their problem so will the students at their seats. When the students at the chalkboard are finished, the next player on their team will go to the chalkboard and check their teammate/s subtraction problem with addition. Students at their seats will do this also. If the subtraction problem was done and checked correctly, that team earns two points. If the subtraction problem was done incorrectly, the player thatís checking it with addition will correct it. One point will be given to that team for this problem. The next player on each team picks a card, writes it on the board, works it out on the board as his/her teammates work it out at their seats, then he/she sits down. The next player checks it with addition on the chalkboard as their teammates check it at their seats. Points will be given to correct answers. After all the cards are done, the team with the most points wins.
5. Take up all the papers the students have been working their problems out on at their seats.
6. Give each child a new piece of paper.
7. Write 10 of the problems from the cards or 10 new subtraction problems on the chalkboard. Students will copy the problems off the board, work them out, and check them with addition.
8. When all the students are done, collect and check their work.
Students who correctly answer 80% of the problems on the chalkboard will have shown mastery of this skill