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8th grade · Math · Unit 15 of 17

Cones, Cylinders & Spheres

Volume of round solids

What your child practices

Using the volume formulas for cylinders, cones and spheres, in terms of π and with 3.14.

Alabama Course of Study content standard: 8.29; 8.30 · using the formulas for the volumes of cones, cylinders and spheres

How we explain it

Children can open this short lesson before they practice.

  1. Cylinder: V = πr²h.
  2. Cone: V = ⅓πr²h, one third of the matching cylinder.
  3. Sphere: V = (4/3)πr³.

Example: A cylinder has radius 3 cm and height 5 cm. What is its volume, in terms of π? r² = 9. 9 × 5 = 45. Answer: 45π cm³

Cones, Cylinders & Spheres in Alabama

In the Alabama Course of Study, this is unit 15 of 17 in 8th grade Math, after Functions and before Slope & Rate of Change.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Alabama State Department of Education (ALSDE)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    A cone has radius 5 in and height 12 in. What is its volume, in terms of π?

    • 100π in³
    • 125π in³
    • 300π in³
    • 40π in³

  2. Question 2

    A cylinder has radius 1 cm and height 9 cm. What is its volume, in terms of π?

    • 9π cm³
    • 18π cm³
    • 36π cm³

  3. Question 3

    A cone and a cylinder have the same base and height. The cylinder holds 75 cm³. How much does the cone hold?

    • 37.5 cm³
    • 225 cm³
    • 72 cm³
    • 25 cm³

  4. Question 4

    A can has radius 2 cm and height 10 cm. Using 3.14 for π, what is its volume in cm³?

    answer boxcm³

  5. Question 5

    A ball has radius 6 cm. What is its volume, in terms of π?

    • 216π cm³
    • 576π cm³
    • 288π cm³
    • 144π cm³

  6. Question 6

    A can has radius 5 cm and height 7 cm. Using 3.14 for π, what is its volume in cm³?

    answer boxcm³

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