Math
Today we continued our discussion of perimeter by looking at the perimeter of rectangles and the relationship between the length and width of a rectangle and its perimeter.

Let's look at the following rectangle:

We can calculate the perimeter by adding the length +length + width + width.

Perimeter = 9 cm + 9 cm + 4 cm + 4 cm
                 = 26 cm

But that isn't the only way we can find the perimeter. We can multiply the length by 2 (double) and multiply the width by 2 (double) and add the two products.

Perimeter = (9 cm x 2) + (4 cm x 2)
                 = 18 cm + 8 cm
                 = 26 cm

We can also add the length and width then multiply the sum by 2 (double)

Perimeter = (9 cm + 4 cm) x 2
                = 13 cm x 2
                = 26 cm

Each of the above equations are called FORMULAS. A formula is a rule that is used to find the answer to a problem. In our example it is a rule to find the perimeter of a rectangle.

Grade 4 must include the third formula when completing homework. This formula is very important when we are trying to find the length when we know the perimeter and width and when we are trying to find all the possible dimensions of rectangles with a given perimeter.

For example, what are all the rectangles with a perimeter of 24 m?

Perimeter = ( l + w) x 2
        24 m= (l + w) x 2
        12 m = 1 + w

So we find all the pairs of numbers that add to 12 m

11 m and 1 m
10 m and 2 m
9 m and 3 m
8 m and 4 m
7 m and 5 m
6 m and 6 m

Another example of how we use this formula....
A rectangle has a perimeter of 32 mm and a length of 10 mm. What is the width of the rectangle?

Perimeter = (l + w) x 2
   32 mm = (l + w) x 2
    16 mm = l + w
    16 mm = 10 mm + w

So the width must be 6 mm to make the equation true.

Writing
Most students worked VERY HARD to complete their story today. Tomorrow you will be conferencing with a peer / classmate to revise and edit your story.

Science
Tomorrow we will be looking at how energy is TRANSFORMED. Our design project for after the March Break is constructing an energy transforming vehicle.



Reminders:

• Adding and subtracting decimal problem solving test on Thursday. See the sample problems on the blog.