3.NBT.2 More Ideas from VDW

I am adding two-three digit numbers. The sum is 825. What might the two numbers be? Explain your thinking.
Write two numbers who have a sum of more than 500 but less than 700 when added together.
List two numbers whose sum is a palindrome.

Good Questions / Problems in Math:
• The difference between two numbers is 21. What might the numbers be?
• How do you know that 560 – 200 is not the same as 200 – 560. Explain your thinking.
• Ask the students to write two subtraction problems (two- digit from two-digit) that have a difference of 24.
• Provide completed subtraction problems with one digit blanked out. For example, you could provide 384 - 229 = 155 with the 2 (in the tens place) missing. Students would then be asked to find the missing number.

Base Ten Block Activity
Use base ten blocks to model adding 2-3 digit numbers that require regrouping. Provide pairs of students with at least 19 of each: hundreds, tens and ones blocks and a place value mat. Write a 2-3 digit addition problem on the chalkboard that requires regrouping such as 257 + 139. Have pairs model and solve using the base 10 blocks. Trading as necessary.

Number Cubes
Partner 1 rolls 2-3 number cubes and records the number. Partner 2 does the same. Partners add their numbers together to find the sum. Find which students have the largest sum and smallest sums in the class. After sharing, have students roll 2-3 number cubes each to make an addition problem with the smallest sum possible. Have students explain their thinking.

Adjusting Numbers
Explain to students how to adjust numbers so that they are adding friendly numbers. For example when adding 57 + 38, think 57 + 40, then subtract 2; when adding 32 + 57, think 57 + 30, then add 2. See “Mental Math in the Primary Grades” for additional ideas.

Build a number and subtract using base ten blocks
Have students make a number (357) using base ten blocks. Have students subtract 18. Discuss what needs to be done in order to subtract 18. (Regrouping one ten, stick to ten ones, dots) Repeat the process with another number. (This can also be done with squares, sticks and dots.)

Destination Zero
Write 100 on the board. Students can have individual whiteboards to work on. Have 6 different students roll 6 different die (Use place value dice or digit cards 0-99. Write each number rolled on the board under 100 (30, 5, 1, 12, 15, 8) One at a time, subtract a number from 100 (100 – 15 for example might be talked through as 15 is 1 ten and 5 ones. Let’s take away the 1 ten first 100-10 = 90. Now, let’s take away 5 ones 90-5 = 85). Continue until all 6 numbers rolled have been subtracted. The game can be repeated with new students rolling, in pairs or groups of 6.

Subtraction on a number line

Pose a problem to the students: Ms. Nelson invited 217 people to her wedding. 59 people said they could not attend. How many people will attend her wedding?
Create a number line on the board and ask students what the two endpoints are for this problem (59 to 217). Write the endpoints on the number line.
Tell students they will find the distance between 59 and 217 to figure out how many people will attend the wedding.
Have students start with 217 and find an easy number/benchmark between that and 59 (such as 200). Explain the distance between 217 and 200 is 17. Mark 200 on the number line and mark 17 above 200 and 217.
Find another benchmark number between 59 and 200 (such as 100). Mark 100 on the number line. The distance between 200 and 100 is 100. Mark 100 above 200 and 100 on the number line.
The next benchmark found may be 60 (the distance is 40) or students might jump right to 59 (the distance is 41).
To find the difference add all the differences together (17 + 100 + 41 = 158).

3.NBT.2 More Ideas from VDW

Ideas Inspired from Teaching Student-Centered Mathematics