RS1 Level G, Lesson 146

We are going to start a new weekly blog. This series is going to be based on questions we get from customers when a lesson or concept gets tangled and help is needed.

Today’s blog is thanks to Joanna and her son, Hunter. They live in Florida and started with Level A and are now working on Level G, aka RightStart™ Mathematics; A Hands-On Geometric Approach.

Here’s Hunter working on Level G, Lesson 146…..G146 Hunter

This lesson is on pyramids. One of the goals of the lesson is to find the surface area and volume of a pyramid. And that’s where we all stalled out, myself included, once we tried to apply the lesson to the worksheet.

This is what we have on the worksheet:

G146 Worksheet 146-1

Constructing the pyramid and drawing the net: no problem. Find the volume and surface area. Now we have a problem!

Let’s start with the surface area. For me, that’s easier. Because I’m the writer here and letting you share in my confusion and subsequent learning, we’re going address this the way my brain thinks!

So, surface area. We need to add up the area of the base and the four triangle sides:G146 surface area formula

The worksheet tells us to use decimeters to two places. Using my handy-dandy ruler, I know the side of a panel is 10 cm or 1 decimeter (dm). So what’s the area of the base of this pyramid? It’s the base times the height, or b × h. That’ll be 1 dm × 1 dm. Area is 1².  That was easy.

Now we need to figure out the area of the triangles. What’s that formula? Area of a triangle is half of the base times the height:G146 triangle area formula

We know the base of the triangle. It’s 1 dm. But we don’t know the height! Let’s look at the picture again.G146 Image

Take a closer look. What are we looking for? We are looking for the area of one of the side panel triangles. Let me draw it out…..G146 Image outline

Looking at the formula, we know the base. It’s the same measurement as the side of the square; 1 dm. Actually, because this is an equilateral triangle, all the sides are 1dm. But the height? We could measure, but that’s not very accurate. I know! Let’s use the Pythagorean Theorem:G146 pythagorean theorem

Divide the triangle in half. This will be our height measurement.G146 Image for height

Now, using the Pythagorean Theorem, we know the measurement of the base, a; it will be half of 1 dm, or .5. The measurement of the hypotenuse, c, is 1. Plugging our numbers into the formula, we have the following:G146 height calculation

Alrighty! Now we have the height of our triangle. Next is the area of the triangle.G146 area triangle

Good. And finally the surface area of the pyramid…..G146 surface area calc

Well, once we figured out how to get the height of the triangles, that wasn’t too bad, right? That was the part that hung me up. The rest was pretty easy.

Now let’s tackle the volume of the pyramid. How do THAT? Well, look back to the lesson. It’s right there!G146 Lesson 146Translation? It’s like this:G146 volume formula

We’re going to use a capital B and H for base and height because these are different measurements than we used for the surface area of the pyramid. Base area is 1 dm × 1 dm, or 1².  We already figured that out, remember? Now for that pesky height measurement again.G146 image for volume

Got any clues? How about this…..G146 Image for volume height

Using the Pythagorean Theorem, we know the base, a; that is half of 1 dm, or .5. The measurement of the hypotenuse, c, is known from our previous calculation of .866. Plugging our numbers into the formula, we come up with the height of the pyramid, or b, as .707. How that we have the height, H, we’re back in business.

And the volume for this pyramid is…..G146 volume calc

So, one more thought for you all. Why, oh why, didn’t the worksheet just give us these measurements? Or at least a clue?? Well, that’s the way real life problems occur. Sometimes we only have one piece of the puzzle, but if we look at other things we know, in this case the Pythagorean Theorem, we can figure out the missing pieces of information with a bit of maneuvering. And we did just that!



  1. Diana DiPersio says:

    Thank you! We are finishing B- hope and pray to continue through.

  2. Sara Stanke says:

    This is going to be so helpful! I am teaching Level G next year to my youngest son. The last time I taught this I ended many days in frusteration, because I couldn’t figure it out. I am so thankful for these helpful blogs!

  3. Wendy Eggert says:

    Love this idea! However, my oldest child has already completed this lesson and my next two are further away from it, and I’m afraid I may not remember all this when my other kiddos get there. Is there any plan of your “filing” these blogs according to level and lesson number so that when we’re stumped, we can look up that particular lesson (which may have been written 2 years prior, by the time I re-teach it)? And, I loved learning in level G (my first child started at A) that you have people we can call for help when we’re stumped! Loved talking to your New Mexico gal in Moriarty/East Mountain area!! We learned we knew each other when our family used to live there!! Great curriculum!!

  4. Christine S. says:

    Thank you so much, we are on level G now, at the beginning.
    thank you for all the work you do to help.

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