“Today we are going to add and subtract two- and three-digit numbers using base-ten blocks.”

Hold up a flat and say, “This is a flat. It represents 100.” Hold up a long and say, “This is a long. It represents 10.” Hold up a cube and say, “This is a cube. It represents 1.”

Write the problem 231 + 146 = on the board.

“I am going to model how I can use base-ten blocks to find the sum of these two numbers. In the number 231 I have 2 hundreds, 3 tens, and 1 one.” As you are saying this, get two flats, three longs, and one cube. “In the number 146 I have 1 hundred, 4 tens, and 6 ones.” As you are saying this, get one flat, four longs, and six cubes. “Now I can join the base-ten blocks and count them to find the sum of 231 + 146.” Model by putting the flats together, the longs together, the cubes together, and then counting the base-ten blocks. Write the sum after the equal sign.

Remind students how to draw base-ten blocks. A square represents a flat, a vertical line represents a long, and a dot represents a cube. Draw this on the board. Now, show students what the above problem would look like using pictures of base-ten blocks rather than the actual base-ten blocks.

Distribute base-ten blocks to each student. Write the problem 257 + 222 = on the board. “Let’s try one together. First we have 257. How many hundreds do we need? (2) How many tens do we need? (5) How many ones do we need? (7) Now we need to make 222. How many hundreds do we need? (2) How many tens do we need? (2) How many ones do we need? (2) Please use your base-ten blocks to find the sum of these two numbers.” Support students as they find the sum of these two numbers. Have a student show the class what s/he did and write the sum after the equal sign.

Write the equation 458 + 123 = on the board. Ask students to use their base-ten blocks to solve this equation. Support students as they find the sum of these two numbers. Have a student show the class what s/he did and write the sum after the equals sign.

“Now, on your whiteboard please show me what this addition problem would look like if you drew pictures of base-ten blocks rather than using the actual base-ten blocks.” Support students as they find the sum by drawing pictures of base-ten blocks rather than using the actual blocks. Have a student show the class what s/he did on his/her whiteboard.

“Not only can we use base-ten blocks to find the sum of two numbers, we can also use base-ten blocks to find the difference of two numbers.” Write 548 – 324 = on the board.

“I am going to model how I can use base-ten blocks to find the difference of these two numbers. My minuend is 548. Remember, ‘minuend’ means the number from which another number is subtracted. In 548, I have 5 hundreds, 4 tens, and 8 ones.” As you are saying this, get five flats, four longs, and eight cubes. “Now I need to take away 324, which is the subtrahend. In this number there are 3 hundreds, 2 tens, and 4 ones. Therefore, I need to take away three flats, two longs, and four cubes. I will count the remaining blocks to find the difference.” Count the remaining blocks and write the difference after the equal sign.

Now, show students what the above problem would look like using pictures of base-ten blocks rather than the actual base-ten blocks. Draw 548 using pictures of base-ten blocks, cross out the blocks that represent 324, and count those remaining.

Write the problem 695 – 381 = on the board. “Please use your base-ten blocks to find the difference of these two numbers. Begin by representing the minuend with base-ten blocks, take the base-ten blocks that represent the subtrahend away, and count the remaining base-ten blocks to find the difference.” Support students as they find the difference of these two numbers. Have a student show the class what s/he did to find the difference using base-ten blocks.

“Now, on your whiteboard please show me what this subtraction problem would look like if you drew pictures of base-ten blocks rather than using the actual base-ten blocks.” Support students as they find the difference by drawing pictures of base-ten blocks to represent the minuend, crossing off the base-ten blocks that represent the subtrahend, and counting the remaining base-ten blocks to find the difference. Have a student show the class what s/he did on his/her whiteboard.

“Now you are going to use base-ten blocks to help you solve addition and subtraction problems. You have eight problems to solve. For four of the problems you will use the actual base-ten blocks to solve the problems. For the remaining four you will draw pictures of base-ten blocks to solve the problems.” Distribute a copy to each student of the Adding and Subtracting Using Base-Ten Blocks Worksheet (M-2-2-1_Adding and Subtracting Using Base-Ten Blocks Worksheet and KEY.docx). Move around the room observing and asking clarifying questions to evaluate which students can add and subtract three-digit numbers, without regrouping, using base-ten blocks and which students need additional exploration.

Extension:

• Routine: Students play Top-It and/or Beat the Calculator. (M-2-2-1_Top-It Directions.docx and M-2-2-1_Beat the Calculator Directions.docx). Students can use base-ten blocks to help them compute. Students can also play games listed in Related Resources.
• Small Group: For students who need additional exploration, pose the following problems: