Volume By The Numbers

Here's the list in order to find volume:

1. What shape is it?

Answering this question helps you decide which formulas to write down.

2. Write formulas

Mr. V counts it wrong if you don't write formulas.

3. Plug in the numbers.

This part can be a little tricky if you see extra numbers.  If you get tripped up by this, I'll explain in detail.

4. Solve.

Finish doing the math.  Some of you are doing these steps so fast you're making mistakes.  Others are having difficulty with step 3 because they have trouble identifying the base.

Let's try some problems:

As you can see this problem has a lot of information on it.  But by following the steps you can eliminate some of the confusion.

Step 1. What shape is it?

This is a triangular prism.  I know this because it has 2 faces that are triangles, and any pyramid must have at least 4 triangles.  Prisms also have rectangular faces.  Everyone see that the rectangular faces are 6 by 12 and 6 by 4?  This means that the height of my prism is 6.

Step 2. Write Formulas

My general formula for prisms is:                           V=Bh
My specific formula for triangular prisms is:            V=(0.5*b*h) * h
The height for my base always forms a right angle with the base.  So 3.9 is the height of the triangular base and 12 is the base of the triangular base.  (sorry for the word confusion, but those are the labels Texas wants us to use.).  I already saw that the height of the prism is 6, because that's the same for all the rectangular faces.

Step 3. Plug in the Numbers.

I described alot above.  The numbers are:              V=(0.5*12*3.9)*6

Step 4. Solve.

12 * 0.5 = 6  (always find an even number to divide by 2 first when dealing with triangular shapes)

5
3.9
* 6
___
23.4

1 2
23.4
* 6
____
130.4

V = 130.4