Since we mastered double-digit addition, it's time to move on to double-digit subtraction. Subtraction is ALWAYS much harder for students than addition, especially when re-grouping (or borrowing) is involved. Just like with learning double-digit addition, we first learned so basic strategies to understand the idea of going backwards. Students worked on hopping back tens and ones on a hundred chart, hopping back tens and ones on an open number line, and counting back tens and ones mentally. We then moved on to the traditional method of subtracting with borrowing (re-grouping). Many students have a hard time not just subtracting right away. For instance, if a student sees 52 - 38, they automatically just want to say that 2-8=6. I then ask students if you have 2, can you take away 6? Or I have them draw it out. Students were introduced to some poems to try to help them remember when they need to borrow and when they can just subtract straight away: "More on top? No need to stop!" Students can just subtract straight away, as they like. "More on the floor? Go next door to get 10 more." I also pretend to knock on the tens place value like it's an apartment next door and say, "Oh Mr. 10, may I borrow one of you to come over please?" That has helped in some instances. "Numbers the same? 0s the game." Again students know that if they have 3 and we're taking away 3, they have 0. This helped many students, but some were still struggling so we used connecting blocks to build place value blocks of tens and ones. Then students could physically see they didn't have enough and have to take one of the tens and break it apart into 10 ones to see that now they have 1 less ten and 10 more ones. Majority of the students have it now, but this will have to be something we continue as with break coming up, it will be easy to forget if they weren't strong in it yet.
0 Comments
We had been working on place value for the last few weeks. Students worked on understanding the value of each number in a place value. For instance, in 325 the 2 means 20 or 2 tens. They also continued learning about standard form, expanded form, word form, and drawing out the place value blocks. We also used place value to help us count patterns. We counted by 10s and 100s from any number: 67, 77, 87, 97, 107....
We are now using what we learned about place value to add double-digit numbers. The way that we have practiced so far is using the partial-sums way. In that way, students take what they learned about place value to help them add the numbers without assistance from their number grid. Partial-sums is basically the breaking apart numbers method we learned. It does a great job of having students understand place value and exactly what they are doing when they regroup and carry the 1. We had them start with the ones place since that is what they will do when they learn the algorithm way (traditional method). Partial-Sums: 45 +37 12 ---> First you add the ones 5 + 7 = 12 +70 --->Then you add the tens: 4 tens (40) + 3 tens (30) = 7 tens, which is 70. 82 ---> Finally you add the tens and ones together. This shows the students what exactly each number means when they are adding. We moved on from learning the partial-sums method of adding double-digit numbers to adding using the traditional algorithm of regrouping. There are quite a few students who are forgetting to add the 1 that we've carried over to the tens place. We've been working on this by writing the answer to the ones place on the side of the ones place (so if it's 36 + 27 then we add 6 +7 and write a 13 on the side) and drawing an arrow from the 1 to the top of the tens place and another arrow from the 3 to the ones place. Then we add the tens together. The more we practice, the better it's getting but it's still a work in progress. |
ArchivesCategories |