Differentiation for Subtraction NBT

Differentiation for Subtraction – NBT.2 Extend - Have each child use friendly numbers in two different ways to find the difference for 201 – 156 =

On Target - Write the following problem on board: 63 – 49 = - Model how to make a friendly number using the number 49: 49 + 1 = 50. Talk about why you also add 1 to 63: 63 + 1 = 64, in order to get the correct difference. - Work together to subtract mentally: 64 – 50 = 14 - Now use number line and two color crayons to show how the jump between 49 and 63 is the same length as the jump between 50 and 64.

Support - Review how to take away tens from different numbers (97, 87, 77, etc) - Next write the example on board: 70 – 30 - How can you subtract the numbers using mental math? - Next write 70 – 32. - Tell students that a strategy to subtract is to take away tens and then ones. - Model how to first take away tens to subtract 30: 70, 60, 50, 40. Then take away ones to subtract 2: 40, 39, 38. What is the difference?

Extend - Have each pair toss the number cube six times and use the digits to write two 3 digit number that can be subtracted without regrouping. - How did you decide where to place the digits? - Repeat for a subtraction prob that needs regroups. - Challenge kids to toss the dice three times to write a 3 digit number. Then have them write two subtraction problems with that number as the difference one problem without regrouping and one with it. On Target - Write 174 – 116 - Provide students with grid paper and guide them to write the problem on paper using the boxes to help them line up the digits. - Point to ones column. Do you need to regroup? Why?

Support - Write 352 – 147 on board. Have students use base ten blocks to show 352. - Can we subtract 7 ones? What can we do? Now let us subtract 4 tens. How many are left? Let us subtract 1 hundred. How many hundreds are left?

Extend - Have each pair toss a dice six times and use those digits to write two 3 digit numbers that can be subtracted using the strategy of combining the tens and ones place. - How did you decide which numbers to use? - If the student can make a problem that can be subtracted by combining tens and ones he or she scores 1 point. - First student who gets 3 points wins.

On Target - Write on board:

- Have them decide whether they can subtract the ones. Explain that there are not enough ones. Discuss the strategy of combining tens and ones. 20 + 4 = 24 and 10 + 9 – 19 - Ask students how they might subtract 19 ones from 24 ones mentally. Suggest counting back or counting one. - Work with kids to record the different of 5 ones and write a 0 for the tens.

Support - Write 31 – 28 on board. - Have students talk about different strategies that can be used to find the answer. - Next write the problem on board: 231 – 128 - Ask students to compare the two problems. Help them see that the number of tens and ones are the same. Ask students how they might use mental math to find the difference - Discuss that the tens and ones can be combined to subtract them mentally. Work with students to use the strategy and find difference.