Addition and Subtraction (Lesson 2)

Let’s focus on whole numbers.

Now we will look at how what we’ve learned in the previous lesson relates to addition and subtraction. For now we will only focus on whole numbers.

You are a painter and you are walking down the road. You painted 2 houses on the right side of the street and 5 houses on the left side of the street. How many houses have you painted? Yes, houses. There are terms that use when adding individual parts.

The parts we add together are called addends and the answer is called the sum. You can sue the dot method or finger method to find the solutions, but you should dedicate time to learn these numbers with speed because as math gets harder, not having an immediate recall of addition will slow you down.

Quiz: Single Digit Speed Test

Part A: Large Numbers

If I ask you to give me the immediate answer for:

You may need a moment to find the sum. Chances are that to get the solution you must do something in your head. Most likely you will rearrange the numbers because when adding or subtracting large numbers the math is not as easy as with single digit numbers.

To start we typically set up an addition of large numbers vertically.

Which is correct? Why?

As we learned before, place values are important! WE must align each digit based on place value.

We are actually thinking of numbers in expanded form and adding each little part, all at once. Be sure to add place values to the same place value. Having neat handwriting helps so that these numbers are not aligned incorrectly.

We must align our numbers by place value or it will not make any sense and we will get the problem wrong. You can do it in you head, but we will write these numbers out.

Steps:

  1. Align vertically.
  2. Only one digit fits in each column so if we have a two digit sum, we must carry the tens digit to the next column. We continue this process until all values are added.

Gives us the following:

In addition we will see how order does not matter. We will go over properties. Just realize that for addition, you will always get the same answer no matter the order.

Part B: Properties

There are some rules you must be aware of when dealing with addition.

What happens if I take 7 and add zero to it?

What happens if we switch the order? This applies to any number added to zero. This is called the addition property of zero or additive identity. We call it an identity because it reflects the number value added where any number added to zero gives us that number back, like a mirror reflection, hence the term ‘identity’.

If I add:

or

This ability to switch order is called the commutative property. Like if you are driving a car, you commute and can switch lanes to get to your destination. Same thing applies here. We can switch the order and still get the same answer for addition.

Does it matter if I rearrange addition?

As you can see, order does not matter. I can rearrange the these numbers in any order, each time I will get a solution of 11. Let’s see what happens if we use parenthesis. Will the order of parenthesis matter? Will we get a different answer? Let’s find out.

The answer was the same in both, so we can say that with parenthesis in addition, order doesn’t matter because addition is commutative. When we use parentheses we now label addition as associative property. Meaning the parenthetical order is associated with the other. With associative property you must realize that parenthesis are being used.

Note: parentheses means “do this section first”

Do we have to add these numbers 2 at a time or is there another way? Yes, we must write addition vertically and keep all digits in the correct position.

Quiz: Can you define the following additional properties?

Now that you understand the properties to addition let’s move on to see the differences of subtraction.

Part C: Subtraction

green applesWe will learn that addition and subtraction can be defined as one another.

Let’s say you have 9 green apples and your friend asks you for 4 apples. If you give away four apples, how many are left?

You need to commit to memory subtraction of single digits of whole numbers with speed and accuracy. As matha advances this will be needed.

Like addition, there are names we give to each part of subtraction math problems.

The first number is called the minuend, the part being taken away is called the subtrahend. We don’t tend to call out these parts often in math problems, but knowing them is good to know.

The answer or solution is called the difference. The difference between two numbers suggests that we are subtracting.

Now let’s look at the properties for subtraction.

Part D: Properties

Subtraction properties have significant differences. Let’s analyze them.

There is not identity property for subtraction

As you can see, if we switch the order of subtraction problems we get different answers. Let’s look at bit further.

Unlike addition, we can say that subtraction is not commutative. Because the order gives us different solutions.

Now lets see what happens with parenthesis.

Associative properties do not work either. We get different answers.If we use parenthesis as a the associative properties rules dictate the regrouping changes our answer. Example:

Like addition, zero taken from a number gives us just that number. Example:

A number subtracted from itself gives us zero, called the property of zero for subtraction.

No other properties apply. Notice that for subtraction, order matters.

Large Numbers

Subtracting large numbers is similar to adding large numbers in that we need to rearrange in vertical form.

Step 1: Align by placing the values vertically. Remember order matters.

Step 2: subtract digit by digit according to place value.

Sometimes the subtraction gets messy and doesn’t come out as we’d like.

When there is not enough to cover, we must borrow a ten and overload the ones place. Then we subtract.

E. Perimeter

If you watch the show Perimeter, you’d hear actors say, “Secure the perimeter.”

What does perimeter mean? Perimeter is the distance around something, called a polygon. Now we need to know what is A polygon? We define polygons as a closed figure with straight sides. Perimeter is not the area, but the outside distance by length.

Can you find the perimeter of this polygon?

Add up all of the sides and use units if given.

What if you were a contractor and decided to visit Home Depot to purchase supplies. You decide that you need 1000 feet of baseboards. You would request it by the perimeter of the room.

What about rectangles? Do you need to measure the the other sides? Why not?

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