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LearningTranscript
00:00Hello guys. Today we are playing with some toys from my bathtub. We are going to learn
00:07about a few things today that are really cool in addition and subtraction. We will use some
00:12of my toys to help us. Let's take a look. Here are some ducks. We have three blue ducks
00:21and seven yellow ducks. Can you tell me how many ducks we have in all? We have ten ducks
00:28all together. When you add three and seven you get ten ducks in all. Now here is something
00:33really cool. The ducks just moved positions. Is the answer still the same? Yes, the answer
00:42is still ten, the same as before. In addition we have what we call the commutative property.
00:50This seems like something difficult to understand but it is not. All it means is that when we
00:55are adding numbers together they can be switched around as much as you want and the answer
00:59will still be the same. This only works for addition so remember that. Here is a math
01:08problem where we can use what we just learned. It says if eight plus two equals ten then
01:13blank plus eight equals ten. We need to fill in the blank with the missing number. We know
01:19that eight plus two equals ten. We just learned that in addition we can switch the eight and
01:26two around and still get the same answer of ten. So to fill in the missing number what
01:31do you think it will be? The missing number is two. The numbers eight and two were just
01:38switched. With the two in the blank we get two plus eight equals ten and that is true.
01:44Great job kids! Here is another math problem but this time
01:50it is subtraction. The problem says if nine subtract four equals five then nine subtract
01:57five equals blank. We need to fill in the blank. The first thing we should know is that
02:03subtraction is not the same as addition. In addition we can switch the numbers around
02:08but not with subtraction. But addition and subtraction are similar in some ways. Let
02:13me show you what I mean. Here is a math mountain. If you are not familiar with a math mountain
02:19that is just fine. At the top we have the total. At the bottom we have what we call
02:25partners or addends. The total is nine and the partners are four and five. We can use
02:32both subtraction and addition with this math mountain. If we add the four and five together
02:38we get the total of nine. We can also subtract. Just like the first part of the problem below.
02:46Nine subtract four equals five. Let's solve the part of the problem we don't know. Nine
02:56subtract five equals what? You probably figured it out but let's use addition to find the
03:04answer. We will start at the partner we know which is five. Let's count up from five until
03:11we get to the total. Starting from five we count six, seven, eight, nine. We counted
03:19four numbers so the other partner is four. Amazing job! I'm sure you can now see that
03:26subtraction and addition are related.
03:31I want to show you one last addition skill. The problem says two plus six plus four equals
03:38twelve is the same as ten plus blank equals twelve. When we are doing addition with more
03:45than two numbers like this it is helpful to make groups of doubles or tens. In this example
03:50we can combine the six and the four together to make ten. Adding with ten is much easier
03:57than trying to add two plus six plus four. Many of you already know partners of ten like
04:03six and four, five and five, three and seven and so on. Now we just have to add two plus
04:11ten which is twelve. It saves us time to combine numbers that make ten and then add the other
04:17numbers. So the blank in this problem should be filled with what number? The answer is
04:25two. Ten plus two equals twelve. Great job again! That was a long lesson but it will
04:33help you as you add and subtract. Thanks for coming. We will see you next time.