A rectangular prism has dimensions 2½ ft × 3 ft × 4 ft. What is its
volume?
Tip: Write 2½ as an improper fraction or decimal: 2½
= 2.5. Then multiply: 2.5 × 3 × 4.
Show your multiplication:
Sentence frame: "I converted 2½ to ___, then multiplied ___ × ___ ×
___ = ___ ft³."
✓Correct! 2.5 × 3 = 7.5, then 7.5 × 4 = 30 ft³.
✗Convert 2½ to 2.5. Then 2.5 × 3 = 7.5 and 7.5 × 4 =
30 ft³. The answer is B.
Practice 3
Sort each measurement into the correct category:
area or volume.
Remember:Area is measured
in square units (cm², ft²). Volume is
measured in cubic units (cm³, ft³).
24 cm³
15 ft²
100 in.³
36 m²
7.5 ft³
50 cm²
Area (square units)
Volume (cubic units)
✓All correct! Area uses square units (²) and volume uses cubic units
(³).
✗Some items are in the wrong group. Square units (²) = area; cubic
units (³) = volume. Try again!
Practice 4
An aquarium is 1½ ft long, 1 ft wide, and 1 ft tall. How many cubic
feet of water can it hold?
Real-world connection: The aquarium is a
rectangular prism. Use V = l × w × h with
the given dimensions. 1½ = 1.5.
Explain your reasoning:
Sentence frame: "V = ___ × ___ × ___ = ___ ft³, so the aquarium
holds ___ cubic feet of water."
✓Correct! V = 1.5 × 1 × 1 = 1.5 ft³.
✗V = 1.5 × 1 × 1 = 1.5 ft³. The answer is
B.
Practice 5
How many ½-inch unit cubes fit inside a rectangular prism that is 3
in. × 2 in. × 1 in.?
Think about it: Each edge is divided into ½-inch
segments. Along 3 in. you fit 6 cubes, along 2 in. you fit 4 cubes,
along 1 in. you fit 2 cubes. Multiply the counts: 6 × 4 × 2.
Explain how you counted:
Sentence frame: "Along the length I fit ___ cubes, along the width
___ cubes, and along the height ___ cubes. ___ × ___ × ___ = ___
cubes."
✗Divide each dimension by ½: 3 ÷ 0.5 = 6, 2 ÷ 0.5 = 4, 1 ÷ 0.5 = 2.
Then 6 × 4 × 2 = 48 cubes. The answer is
D.
★
Challenge
1 question
Challenge
A shipping box is 2½ ft long, 1½ ft wide, and 2 ft high. A smaller box
is 1 ft × 1 ft × 1 ft. What is the maximum number of smaller boxes
that fit inside the shipping box?
Think about it: First find the volume of the shipping
box: V = 2.5 × 1.5 × 2. Then think about how the 1 ft³ cubes
physically fit along each dimension (you can only fit whole boxes).
Maximum boxes =
Explain your reasoning:
Sentence frame: "Along 2½ ft I can fit ___ whole boxes, along 1½ ft
I can fit ___ whole box(es), and along 2 ft I can fit ___ whole
boxes. ___ × ___ × ___ = ___ boxes."
✓Correct! Along 2½ ft: 2 boxes. Along 1½ ft: 1 box. Along 2 ft: 2
boxes. 2 × 1 × 2 = 4 boxes. (The leftover space is wasted.)
✗You can only fit whole boxes. 2½ ft fits 2 boxes, 1½ ft fits 1 box,
2 ft fits 2 boxes. 2 × 1 × 2 = 4 boxes.