Grade 8 Volume: Volume of Cylinders

Worked examples

Real problems from the practice worksheets, solved one step at a time.

1. Example 1

   A cylinder has diameter 14 in and height 14 in. What is its volume in cubic inches? Use π ≈ 3.14.

   1. Volume of a cylinder = π × r² × h, with π ≈ 3.14.
   2. The radius is half the diameter: 14 ÷ 2 = 7.
   3. r² = 7 × 7 = 49, and 49 × 14 = 686.
   4. 3.14 × 686 = 2154.04. The volume is 2154.04 cubic inches.

   Answer: 2154.04

2. Example 2

   A cylinder has radius 5 in and height 10 in. What is its volume in cubic inches? Use π ≈ 3.14.

   1. Volume of a cylinder = π × r² × h, with π ≈ 3.14.
   2. r² = 5 × 5 = 25, and 25 × 10 = 250.
   3. 3.14 × 250 = 785. The volume is 785 cubic inches.

   Answer: 785

3. Example 3

   A cylinder has a volume of 1130.4 cubic feet and a radius of 6 ft. What is its height in feet? Use π ≈ 3.14.

   1. V = π × r² × h, so h = V ÷ (π × r²).
   2. Base area: 3.14 × 6 × 6 = 3.14 × 36 = 113.04.
   3. 1130.4 ÷ 113.04 = 10. The height is 10 feet.

   Answer: 10