Identify and use a faster way to find the volume of a rectangular prism
While you discuss the Investigation activity below with a partner (or with others in your class), be sure to correctly use the vocabulary terms below.
When we find the volume of a solid shape, we are basically figuring out how many little unit cubes would fit inside the whole space. Just as when we were finding the area of a twodimensional shape we were calculating how many unit squares would fit inside its boundary.
If the following cube was 1 cubic unit, say 1 cm^{3}.
Then, in this activity, we will begin by calculating the volume of the following solids by counting the number of unit cubes. The image below demonstrates which part of each diagram should be used to determine each dimension.
The image below shows a rectangular prism with length 5 units, breadth 3 units, and height 2 units. Notice that the measure of each edge corresponds to the number of unit cubes that could be lined up side by side along that edge.





1. Refer to the diagrams above to complete the table below.
Figure  length  width  height  Volume 

Figure A  5  3  2  30 
Figure B  
Figure C  
Figure D  
Figure E  
Figure F 
2. Is there any relationship between the three numbers that you included for the length, width and height in the table and the Volume of the rectangular prism in the given diagram? Turn and Talk to a partner about the answers that you included in the table and any patterns that you noticed.
3. Next, consider only the base of the rectangular prisms in each of the diagrams. The base of the rectangular prism is the rectangular face that is on the bottom. Count the unit squares in the base in order to determine the area of the Base of the rectangular prism and complete the table below.
Figure  Area of the Base  height  Volume 

Figure A  
Figure B  
Figure C  
Figure D  
Figure E  
Figure F 
4. Is there any relationship between the area of the base, the height and the volume of a rectangular prism? Turn and Talk to a partner about the answers you included in the table and any patterns that you noticed.
5. Using some combination of the variables defined below, can you write one formula that you could use in order to determine the volume of a rectangular prism more quickly than by counting the unit cubes?
6. Do you think that there is a second formula that you can write, using some combination of the variables listed below in order to quickly determine the volume of a rectangular prism? Turn and talk to a partner about the two formulas that you determined. Be sure to explain what each part of your formula actually represents in a diagram (such as Figure A) during your discussion.
Find the volume of a right rectangular prism with fractional edge lengths by packing it with unit cubes of the appropriate unit fraction edge lengths, and show that the volume is the same as would be found by multiplying the edge lengths of the prism. Apply the formulas V = l w h and V = B h to find volumes of right rectangular prisms with fractional edge lengths in the context of solving realworld and mathematical problems.