Let’s look at:
Solving addition and subtraction problems within 1000 in different ways
In Second Grade, we are now efficiently applying strategies to add and subtract, especially strategies based on place value. We’ve worked on Math Practice 1: Making sense of problems and persevering in solving them. Our thinking is “When given a problem, I can make a plan, carry out my plan and check my answer.” To check my answer, I ask myself “Is there another way to solve this problem?” Our learning targets are:
· I can choose when to use addition and/or subtraction in a word problem
· I can represent addition and subtraction word problems using objects, drawings, and equations
Solving word problems requires perseverance, one of our important math traits to remember and use!
The second graders will solve these word problems by using the expanded form, as well as using place value on the HTO (hundreds/tens/ones) chart. They are encouraged to check their answers with their bundles of straws. Please consult the following images for information.
Don’t forget to ask:
How do you know you’re right?
Math Practice 1: Making sense of problems and persevering in solving them.
Addition and subtraction using expanded form and using place value on the HTO chart
A. For addition using the expanded form
- Write numbers in expanded form
- Add up ones, then tens, and then hundreds
- f necessary, to make addition easier, put sums into expanded form as well (here it was done with 14, the sum or 9 and 5).
- Add up all numbers underneath the line to get final answer.
B . For subtraction using the expanded form:
- Write numbers in expanded form
- Regroup numbers if necessary in order to subtract. Rename the numbers by crossing off original numbers and writing new value above. In this example, the 21 of 721 was regrouped into 10 plus 11 in order to facilitate subtraction.
- Add up all numbers underneath the line in order to get final answer.
C. For addition using the HTO chart and place value:
- Write numbers vertically within HTO chart; draw a line underneath
- Add up the ones. (If the sum is greater than nine, put the two digits in their corresponding column on chart).
- Add up the tens, and write that sum on the chart slightly below where sum of ones was written
- Add up the hundreds, writing that number slightly below sum of tens has been written. The numbers will form a “3-layer number” similar to a three layer cake. Draw a line underneath.
- Finally, add up those three numbers to find the sum.
D. For subtraction using the HTO chart and place value:
- Rewrite the numbers vertically within the HTO chart, and draw a line underneath
- Regroup numbers if necessary in order to subtract. Rename the numbers by crossing off original numbers and writing new value above. In this example, the 41 of 541 was regrouped into 30 plus 11 in order to facilitate subtraction.
- Do the subtraction in the ones column, writing down answer in ones column.
- Do subtraction in tens column, writing answer slightly lower in HTO chart in tens column (if digits are greater than nine, put them in the proper column)
- Do subtraction in hundreds column, writing answer slightly lower in HTO chart in hundreds column (if digits are greater than nine, put them in the proper column). Draw a line underneath.
- Add up the three numbers to get final answer.
The Second Grade Team