Friday's Class

...or will it be Monday's class?! Dun dun DUUUUNNNN... :)

(I wonder if we'll have snow/ice tomorrow?)

Please check your answers for the last page in yesterday's Perimeter packet (pg. 191):

1) About 2,090 km

2) 39 in.

3) 48.5 ft

4) 24 ft

5) 1,840 yd

6) 130.72 in.

7) 43.701 in.

8) 0.916 m

If you had any problems with finding the answer, please leave me a comment below. 

Please turn your packets in (place them in the Inbox). 

Today we're going to be taking a look at Circumference. Circumference is the distance around a circle. Check out this diagram from kidsmathgamesonline.com:

Diameter (d) is the distance a cross a circle through its center. 

Radius (r) is the distance from the center to any point on a circle. 

And, as we said, Circumference (c) is the distance around a circle. 

There's a formula to figure out what the Circumference of a circle is:

C = πd 

This says "Circumference = pi times the diameter"

What is that little symbol? That "pi" thing??? Well, it's not a pie, although I could certainly go for a cherry pie right now. 

tasteofhome.com

Anyway. Pi is a number that we use to find Circumference. Use a calculator to find the real value of pi by pressing the  π  button on your calculator. It goes on forever - so we round it to 3.14. 

Now that we know what pi is, we can find the circumference of any circle as long as we know it's diameter. Let's say we have a circle with a diameter of 4.5 inches. All we need to do is plug the numbers into the formula:

C = 3.14 x 4.5

Then, using your calculator or your multiplying decimal method, solve for C:

C = 14.13

We know that the circumference is 14.13 inches. 

There's another way to find Circumference - this time, using radius. Take a look at the circle diagram above. Did you notice that the radius is exactly half the length of a circle's diameter? So to find the Circumference of a circle using the radius, we use the following formula:

C = 2πr

This says "Circumference equals 2 times pi times the radius of a circle."

Again, all we have to do is plug the numbers in. If we have a circle with a radius of 38 ft, we would plug the numbers in like so:

C = 2 x 3.14 x 38

Now solve for C.

C = 238.64 ft.

Once you know the formulas, and remember that pi = 3.14, you're good to go. 

Please read through the bottom of pg. 161 through pg. 162. Then, using a calculator (or by hand), complete questions 9 - 18 on pg. 163. 

You will be turning this in. Please place in the inbox when finished. 

Have a fantastic weekend everyone!